WO2021078128A1

WO2021078128A1 - Method for preparing mesoporous carbon supported metal nanoparticle catalyst

Info

Publication number: WO2021078128A1
Application number: PCT/CN2020/122302
Authority: WO
Inventors: 王光辉; 董超
Original assignee: 中国科学院青岛生物能源与过程研究所
Priority date: 2019-10-22
Filing date: 2020-10-21
Publication date: 2021-04-29
Also published as: CN112691659A; CN112691659B

Abstract

A method for preparing a mesoporous carbon supported metal nanoparticle catalyst. According to the method, a mesoporous carbon supported metal nanoparticle catalyst can be synthesized in two steps of hydrothermal process and carbonization. In the hydrothermal process, a uniform solution is prepared by dispersing a surfactant, an additive, a metal salt precursor (one, two, or three of Pd, Au, Pt, Ag, Ru, Rh, Ir, Ni, Co, Zn, and Cu), and a polymer precursor in a water phase, and the solution is further heated to form a composite material of a mesoporous polymer supported metal precursor; in the carbonization process, the composite material of the polymer supported metal precursor is converted into a mesoporous carbon supported metal nanoparticle catalyst by adjusting a carbonization temperature, a protective atmosphere, etc. By means of the method, a highly dispersed supported catalyst having a uniform metal particle size can be obtained. The method has a simple preparation process, is easy to scale up, and has universality. The obtained catalyst has broad application prospects in the fields such as catalytic hydrogenation, oxidation, and electrochemistry.

Description

Method for preparing mesoporous carbon supported metal nano particle catalyst

Technical field

The invention relates to a mesoporous carbon-supported metal nanoparticle catalyst, which constructs a highly dispersed supported catalyst with a uniform metal particle size through two steps of hydrothermal and carbonization. The obtained catalyst has a wide range of fields such as catalytic hydrogenation, oxidation, electrochemistry, etc. Application prospects.

Background technique

Most reactions in modern industry involve heterogeneous catalysis. Supported metal catalysts are an important type of heterogeneous catalysts that are widely used in petrochemical, biomedicine, aerospace and other fields. In recent years, the application of metal catalysts in the fields of biomass conversion and electrocatalysis has also developed rapidly.

Generally, metal nanoparticles with a size of 3 to 5 nm and a uniform composition will show better catalytic performance. However, the smaller the size of the metal nanoparticles, the greater the surface free energy, and therefore the stability is poor. It is easy to accumulate and grow or lose to cause catalyst deactivation, which is a problem that limits the application of supported metal catalysts with smaller metal nanoparticles (Chem.Rev.2018,118,4981-5079; Adv.Mater.,2019,31, 1803966; Chem. Soc. Rev., 2017, 46, 4774-4808). Controlling the size and distribution of metal nanoparticles and limiting their loss in the catalytic reaction is the key to determining the application performance of metal catalysts. The metal catalyst prepared by the traditional impregnation or co-precipitation method can improve the stability of the metal catalyst through the strong interaction between the metal and the support, but the metal particle size and distribution are often difficult to accurately control; the solvothermal method can synthesize smaller and uniform size However, the weak interaction force between the metal nanoparticles and the carrier when the metal nanoparticles are deposited on the surface of the carrier by colloidal deposition can easily cause the metal nanoparticles to fall off or lose, especially in some harsh multiphase reaction conditions (high temperature and high pressure). , Liquid phase conditions, etc.), it is easier to cause the loss of catalytic active components.

It can be seen that it is necessary to find a new type of universally applicable high-dispersion supported metal catalyst controllable preparation technology to obtain a catalyst with a uniform metal particle size, simplify the preparation process, and be easy to scale-up production for industrial application.

Summary of the invention

In order to solve the above-mentioned control of the size of metal nanoparticles and the catalyst deactivation caused by the loss in the catalytic reaction process, the present invention provides a method for preparing a highly dispersed supported metal catalyst. This method adopts hydrothermal and carbonization methods. The mesoporous carbon-supported metal nanoparticle catalyst is constructed in a two-step process. By introducing metal salt precursors during the synthesis process, the pore structure of the carrier is used to confine the growth of metal nanoparticles, which can effectively control the size of metal nanoparticles and protect the metal nanoparticles. Prevent its loss during the reaction.

The present invention provides a method for preparing a mesoporous carbon-supported metal nanoparticle catalyst, including: providing an aqueous solution containing aromatic compounds, aldehyde compounds, metal salt precursors, surfactants, and additives; heating the aqueous solution, A composite material with a mesoporous polymer supporting a metal precursor is obtained; the obtained composite material can be subjected to a carbonization process to obtain a mesoporous carbon supporting metal nanoparticle catalyst.

The aromatic compound in the preparation method must contain at least one hydroxyl group. The aromatic compound can be a phenyl compound, a naphthyl compound or an anthracene compound, such as phenol, resorcinol, aminophenol, p-hydroxybenzoic acid, 2, One or more of 4-dihydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 3,7-dihydroxy-2-naphthoic acid, etc.

The aldehyde compound is one or more selected from aliphatic C1 to C12 fatty aldehydes, such as formaldehyde, acetaldehyde, crotonaldehyde, aromatic aldehydes such as furfural, or one or more compounds that can be decomposed into formaldehyde, such as six Methylenetetramine or paraformaldehyde.

The molar ratio of the aldehyde compound to the aromatic compound is between 0.1:1 and 10:1, preferably between 0.5:1 and 5:1.

The metal precursor salt can be selected from one, two or three mixtures of Pd, Au, Pt, Ag, Ru, Rh, Ir, Ni, Co, Zn, and Cu, corresponding to single metal catalysts, bimetallic catalysts or Three metal catalysts.

The metal precursor salt can be selected from one, two or three mixtures of nitrate, acetylacetonate, halide, cyanide, acetate, and carbonyl salt.

The molar ratio of the metal precursor salt to the aromatic compound is between 1:1 and 1:10000, preferably between 1:10 and 1:1000, and more preferably between 1:5 and 1:500.

In the preparation of the bimetallic catalyst, two different metal precursor salts are used, which can be mixed in any ratio.

In the preparation of the trimetallic catalyst, three different metal precursor salts are used, which can be mixed in any ratio.

The surfactant is selected from one or more of the amphiphilic block copolymers, where the copolymer needs to satisfy that the hydrophobic segment part contains at least three carbon atoms, such as poly(ethylene oxide)-poly(epoxy) Propane)-poly(ethylene oxide), preferably Pluronic F127 or P123.

Additives are selected from C3 to C30 compound molecules containing amino, mercapto, carboxyl and hydroxyl groups, such as oleic acid, oleylamine, 2-methylimidazole, melamine, pyrrole, pyridine, quinoline, mesitylene, toluene, ethyl One or more of benzene, 2-ethylaniline, thiourea, ethyl 3-mercaptopropionate, thiopropionamide, and thioacetamide.

The molar ratio of surfactant to additive is between 1000:1 and 10:1, preferably between 500:1 and 10:1, and more preferably between 100:1 and 10:1.

The heating temperature of the aqueous solution is 40°C-200°C, preferably 60°C-150°C.

The heating time of the aqueous solution is 1 hour to 48 hours, preferably 4-24 hours.

The carbonization temperature is selected from the range of 150-1000°C, preferably the range of 200-800°C, and more preferably the range of 400-800°C.

The carbonization atmosphere is _{a mixed gas of Ar, N 2} , He or H ₂ and other inert atmospheres.

Monometallic, bimetallic, and trimetallic catalysts can all be prepared by the methods described above.

As described above, the present invention provides a method for preparing a mesoporous carbon-supported metal nanoparticle catalyst, which can synthesize a mesoporous carbon-supported metal nanoparticle catalyst through two steps of hydrothermal and carbonization. Among them, in the hydrothermal synthesis process, the first step is to combine one or two of surfactants, additives, metal salt precursors (Pd, Au, Pt, Ag, Ru, Rh, Ir, Ni, Co, Zn, Cu). One or three), the polymer precursor is dispersed in the water phase to prepare a uniform solution, and the solution is further heated to form a mesoporous polymer supported metal precursor composite material; in the carbonization process, by adjusting the carbonization temperature, protective atmosphere, etc. , Convert the polymer-supported metal precursor composite material into a mesoporous carbon-supported metal nanoparticle catalyst.

The method of the present invention can obtain a highly dispersed supported catalyst with a uniform metal particle size. The preparation process is simple, easy to scale up, and has universal applicability. The obtained catalyst has a wide range of applications in the fields of catalytic hydrogenation, oxidation, electrochemistry, etc. prospect.

Additional aspects and advantages will be partly explained in the following description, part of the content is obvious from the description, or can be learned through actual operations.

Description of the drawings

Figure 1 is a schematic diagram of preparing a mesoporous carbon supported metal nanoparticle catalyst.

2 is a TEM image of the mesoporous carbon supported palladium nanoparticle catalyst prepared in Example 1.

3 is an SEM image of the mesoporous carbon supported palladium nanoparticle catalyst prepared in Example 1. FIG.

4 is an XRD picture of the mesoporous carbon supported palladium nanoparticle catalyst prepared in Example 1.

5 is a physical diagram of the mesoporous carbon supported palladium nanoparticle catalyst prepared in Example 1.

Detailed ways

The present invention relates to a method for preparing a mesoporous carbon-supported metal nanoparticle catalyst, which is described in detail as follows.

First, aromatic compounds, aldehyde compounds, metal salt precursors, surfactants, and additives are dispersed in the water phase to prepare a uniform solution.

The aromatic compound of the present invention is preferably an aromatic compound capable of polymerizing with an aldehyde compound, such as an aromatic compound containing at least one active group such as an amino group or a hydroxyl group. Among the various active groups, the aromatic compound of the present invention preferably contains at least one hydroxyl group. This is because the hydroxyl group can avoid the residue of impurity elements after the later carbonization treatment.

Therefore, preferably, the aromatic compound needs to contain at least one hydroxyl group, and the aromatic compound can be a phenyl compound, a naphthyl compound or an anthracenyl compound, such as phenol, resorcinol, aminophenol, p-hydroxybenzoic acid, One or more of 2,4-dihydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, 3,7-dihydroxy-2-naphthoic acid, etc.

The aldehyde compound is preferably one or more aliphatic C1 to C12 fatty aldehydes, such as formaldehyde, acetaldehyde, crotonaldehyde, aromatic aldehydes such as furfural, or one or more compounds that can be decomposed into formaldehyde , Such as hexamethylenetetramine or paraformaldehyde.

The metal precursor salt is a mixture of one, two or three of Pd, Au, Pt, Ag, Ru, Rh, Ir, Ni, Co, Zn, and Cu, corresponding to a single metal catalyst and a bimetal catalyst, respectively Or three metal catalysts.

The molar ratio of the metal precursor salt to the aromatic compound is between 1:1 and 1:10000. When the molar ratio of the metal precursor salt to the aromatic compound is less than 1:1, the metal loading is extremely high and the size of the metal nanoparticles is difficult to control; when the molar ratio of the metal precursor salt to the aromatic compound is less than 1:10000, the metal The load is extremely low and not suitable for actual production applications. Further preferably, the molar ratio of the metal precursor salt to the aromatic compound is further preferably between 1:10 and 1:1000, more preferably between 1:5 and 1:500.

When preparing the bimetallic catalyst, the precursor salts of the two different metals can be mixed in any ratio.

When preparing the trimetallic catalyst, the precursor salts of the three different metals can be mixed in any ratio.

In the present invention, the surfactant is used as the pore former of the carrier to form a mesoporous structure. The surfactant is selected from one or more of the amphiphilic block copolymers, and the copolymer needs to satisfy that the hydrophobic segment part contains at least three carbon atoms, such as poly(ethylene oxide)-poly(epoxy) Propane)-poly(ethylene oxide), preferably Pluronic F127 or P123.

The added amount of the surfactant is 0.001 times to 100 times, preferably 0.01 times to 10 times, by mass of the aromatic compound containing at least one hydroxyl group. When the amount of surfactant is less than 0.001 times, the carrier cannot form mesopores; when the amount of surfactant is more than 100 times, the polymerization rate of the carrier is slow and the economic cost is higher.

In the present invention, in order to promote uniform dispersion of the metal, additives are used. The additives of the present invention use small organic molecular compounds. We have found that additives have the functions of expanding holes and stabilizing micelles, and can make the metal particles uniformly dispersed. If no additives are added, agglomerated large particles may be formed or cannot be loaded. The additives are preferably C3 to C30 compound molecules containing amino, mercapto, carboxyl and hydroxyl groups, such as oleic acid, oleylamine, 2-methylimidazole, melamine, pyrrole, pyridine, quinoline, mesitylene, toluene, ethyl One or more of benzene, 2-ethylaniline, thiourea, ethyl 3-mercaptopropionate, thiopropionamide, and thioacetamide.

Then, the solution containing aromatic compounds, aldehyde compounds, metal salt precursors, surfactants, and additives is heated, and a mesoporous polymer supporting metal precursor composite material is obtained through a hydrothermal process.

The solution is heated in one step to form a mesoporous polymer-supported metal precursor composite material. The solution heating temperature is preferably 40°C to 200°C. When the heating temperature is lower than 40°C, the polymerization speed is slow, and the support is not easy to form; when the heating temperature is higher than 200°C, the support is rapidly formed, and the metal salt is rapidly reduced to obtain a catalyst with uneven size distribution of metal nanoclusters. Further, the solution heating temperature is more preferably 60°C to 150°C.

The heating time of the solution is preferably at least 1 hour, more preferably at least 4 hours, in order to achieve sufficient heating polymerization. Considering the colloidal state, it generally does not exceed 48 hours, preferably not more than 24 hours. The specific heating time may be adjusted according to the heating temperature and the composition of the solution.

Finally, the mesoporous polymer-supported metal precursor composite material is transformed into a mesoporous carbon-supported metal nanoparticle catalyst through a carbonization process.

The carbonization temperature is selected from the interval of 150-1000°C, preferably the interval of 200-800°C, and further preferably the interval of 400-800°C.

The carbonization time at the carbonization temperature is preferably 1-15 hours, more preferably 2-6 hours. In order to achieve sufficient carbonization, the carbonization time is generally at least 1 hour, and more preferably at least 2 hours. Considering the cost of energy consumption, it generally does not exceed 15 hours, preferably does not exceed 10 hours, and more preferably does not exceed 8 hours.

The carbonization process atmosphere can be selected from Ar, N ₂ , He, or _{a mixed gas of H 2} and other inert atmospheres.

The synthesized catalyst can be characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), etc.

The mesoporous carbon-loaded metal nanoparticle catalyst obtained by the method of the present invention has the characteristics of uniform metal particle size distribution and not easy to lose. It can be prepared only through two steps of hydrothermal and carbonization. The preparation process is simple, easy to scale, and has the advantages of Universality, can have a wide range of application prospects in the fields of catalytic hydrogenation, oxidation, electrochemistry, etc.

In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. .

The present invention can synthesize multiple single metal, bimetal and trimetal catalysts by transforming and combining different types of metal precursors, and the preparation process is shown in FIG. 1. Taking the synthesis of platinum catalyst or palladium catalyst as an example, the metal salt is one of potassium chloroplatinite, potassium chloroplatinite, and platinum acetylacetonate, and the amount is 0.01 mmol to 0.5 mmol. P123 or F127 is used as a surfactant, with a mass of 0.1-10g. 2,4-Dihydroxybenzoic acid or resorcinol is used as the carrier precursor, with a mass of 0.1-5g. The additive uses one of oleic acid, oleylamine, polypropylene glycol 1000, toluene, and chlorobenzene, and the mass is 0.1-15g. The whole system is dissolved in 20-1000ml water to form a homogeneous solution. The mesoporous carbon-supported metal nanoparticle catalyst was synthesized through the following various reaction conditions.

Example 1

Dissolve 3.0g of 2,4-dihydroxybenzoic acid, 0.9g of hexamethylenetetramine, 0.15g of oleic acid, 3.5g of P123 and 0.25mmol of potassium chloropalladite in 80mL of water to form a homogeneous solution, and react at 130°C for 4 hours After the reaction is completed, suction filtration, washing, drying, and carbonization at 500° C. for 4 hours in an argon atmosphere to obtain a mesoporous carbon supported palladium nanoparticle catalyst (shown in Figure 2-TEM, Figure 3-SEM, and Figure 4-XRD).

In addition, the catalyst obtained by the method of the present invention is naturally formed during the preparation process. For example, it is naturally formed during the heating process of the aqueous solution. If the aqueous solution is placed in a glass tube and heated and polymerized, it will naturally obtain a cylindrical catalyst, and if it is placed in a watch glass and heated and polymerized, it will naturally obtain a cake-type catalyst. As shown in Fig. 5, it is the columnar mesoporous carbon supported palladium nanoparticle catalyst obtained by natural forming.

Therefore, the catalyst prepared by the present invention can be easily shaped arbitrarily, and the catalysts in various shapes such as powder, column, flake, etc. can be conveniently prepared.

Example 2

Dissolve 3.0g 2,4-dihydroxybenzoic acid, 0.9g hexamethylenetetramine, 0.3g polypropylene glycol 1000, 3.5g P123 and 0.25mmol platinum acetylacetonate in 80mL water to form a homogeneous solution, and react at 130°C for 4 hours. After the reaction is completed, suction filtration, washing, drying, and carbonization at 500° C. for 4 h in an argon atmosphere, to obtain a mesoporous carbon-supported platinum nanoparticle catalyst.

Example 3

Dissolve 3.0g 2,4-dihydroxybenzoic acid, 0.9g hexamethylenetetramine, 0.22g oleylamine, 3.5g P123, 0.25mmol platinum acetylacetonate in 80mL water to form a homogeneous solution, and react at 130°C for 4 hours. After completion, suction filtration, washing, drying, and carbonization at 500° C. for 4 h in an argon atmosphere, to obtain a mesoporous carbon-supported platinum metal nanoparticle catalyst.

Example 4

Dissolve 3.0g 2,4-dihydroxybenzoic acid, 0.9g hexamethylenetetramine, 0.2g toluene, 3.5g P123 and 0.25mmol potassium chloropalladite in 80mL water to form a homogeneous solution, and react at 130°C for 4 hours. After the reaction is completed, suction filtration, washing, drying, and carbonization at 500° C. for 4 h under an argon atmosphere to obtain a mesoporous carbon-supported palladium nanoparticle catalyst.

Example 5

Dissolve 3.0g 2,4-dihydroxybenzoic acid, 0.9g hexamethylenetetramine, 0.5g chlorobenzene, 3.5g P123 and 0.25mmol potassium chloroplatinate in 80mL water to form a homogeneous solution, and react at 130°C for 4 hours After the reaction is completed, suction filtration, washing, drying, and carbonization at 500° C. for 4 hours in an argon atmosphere to obtain a mesoporous carbon-supported platinum metal nanoparticle catalyst.

Example 6

Dissolve 3.0g resorcinol, 0.9g hexamethylenetetramine, 0.15g oleic acid, 3.5g P123 and 0.25mmol potassium chloropalladite in 80mL water to form a homogeneous solution, react at 130°C for 4 hours, after the reaction is complete , Suction filtration, washing, drying, carbonization at 500°C for 4h under argon atmosphere to obtain mesoporous carbon supported palladium metal nanoparticle catalyst.

Example 7

Dissolve 3.0g resorcinol, 0.9g hexamethylenetetramine, 0.15g oleic acid, 3.5g F127 and 0.25mmol potassium chloropalladite in 80mL water to form a homogeneous solution, react at 130°C for 4 hours, after the reaction is complete , Suction filtration, washing, drying, carbonization at 500°C for 4h under argon atmosphere to obtain mesoporous carbon supported palladium metal nanoparticle catalyst.

Through the above description, the present invention has clearly disclosed the preparation conditions of the catalyst of the present invention. However, it is clear to those skilled in the art that some modifications and improvements can be made to the present invention. Therefore, as long as it does not depart from the spirit of the present invention, any modifications and improvements made to the present invention should fall within the scope of the present invention.

Claims

A method for preparing a mesoporous carbon-supported metal nanoparticle catalyst, the specific process includes:

a) Provide an aqueous solution containing aromatic compounds, aldehyde compounds, metal salt precursors, surfactants, and additives,

b) Heating the solution in a) to obtain a mesoporous polymer supported metal precursor composite material,

c) Wash and dry the composite material obtained in b), and obtain a mesoporous carbon-supported metal nanoparticle catalyst through a carbonization process.
The method for preparing a catalyst according to claim 1, wherein the aromatic compound in step a) contains at least one hydroxyl group, and the aromatic compound is preferably a phenyl compound, a naphthyl compound or an anthracenyl compound, such as phenol, One or more of resorcinol, aminophenol, p-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, and 3,7-dihydroxy-2-naphthoic acid.
The method for preparing a catalyst according to claim 1 or 2, characterized in that the one aldehyde compound in step a) is one or more selected from aliphatic C1 to C12 fatty aldehydes, such as formaldehyde, acetaldehyde, Crotonaldehyde, aromatic aldehydes such as furfural, or one or more compounds that can be decomposed into formaldehyde, such as hexamethylenetetramine, paraformaldehyde.
The method for preparing a catalyst according to any one of claims 1 to 3, characterized in that in step a), the molar ratio of the aldehyde compound to the aromatic compound is between 0.1:1 and 10:1, preferably Between 0.5:1 and 5:1.
The method for preparing a catalyst according to any one of claims 1 to 4, wherein the metal precursor salt in step a) contains Pd, Au, Pt, Ag, Ru, Rh, Ir, Ni, Co A mixture of one, two or three of Zn, Cu, corresponding to single metal catalyst, bimetal catalyst or trimetal catalyst respectively.
The method for preparing a catalyst according to any one of claims 1 to 5, wherein the metal precursor salt in step a) can be selected from the group consisting of nitrate, acetylacetonate, halide, cyanide, and acetic acid. A mixture of one, two or three of salt and carbonyl salt.
The method for preparing a catalyst according to any one of claims 1 to 6, characterized in that the molar ratio of the metal precursor salt to the aromatic compound in step a) is between 1:1 and 1:10000, preferably Between 1:5 and 1:500.
The method for preparing a catalyst according to any one of claims 5 to 7, characterized in that in step a), two different metal precursor salts are mixed in any ratio to finally prepare a bimetallic catalyst.
The method for preparing a catalyst according to any one of claims 5 to 7, characterized in that in step a), three different metal precursor salts are mixed in any ratio to finally prepare a trimetallic catalyst.
The method for preparing a catalyst according to any one of claims 1 to 9, characterized in that in step a), the surfactant is selected from one or more of the amphiphilic block copolymers, and the copolymers need to meet The hydrophobic segment part contains at least three carbon atoms, such as poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), preferably Pluronic F127 or P123.
The method for preparing a catalyst according to any one of claims 1 to 10, characterized in that in step a), the additive is selected from C3 to C30 compound molecules containing amino, mercapto, carboxyl or hydroxyl groups, such as oleic acid, oil Amine, 2-methylimidazole, melamine, pyrrole, pyridine, quinoline, mesitylene, toluene, ethylbenzene, 2-ethylaniline, thiourea, ethyl 3-mercaptopropionate, thiopropionamide, sulfur One or more of acetamide.
The method for preparing a catalyst according to any one of claims 1 to 11, wherein the molar ratio of the surfactant to the additive in step a) is between 1000:1 and 10:1, preferably 100:1 To 10:1.
The method for preparing a catalyst according to any one of claims 1 to 12, characterized in that the heating temperature of the aqueous solution in step b) is 40°C to 200°C, preferably 60°C to 150°C.
The method for preparing a catalyst according to any one of claims 1 to 13, characterized in that the heating time of the aqueous solution in step b) is at least 1 hour, preferably at least 4 hours.
The method for preparing a catalyst according to any one of claims 1 to 14, characterized in that the carbonization temperature in step c) is selected from the range of 150-1000°C, preferably the range of 200-800°C.
The method for preparing a catalyst according to any one of claims 1 to 15, characterized in that the carbonization atmosphere in step c) is a mixed gas of Ar, N 2 , He or H 2 and other inert atmospheres.