CN107537565B - Amphoteric cross-linked polymer supported noble metal catalyst and preparation and alcohol oxidation method - Google Patents

Abstract

The invention discloses a noble metal nanoparticle catalyst loaded by an acid-base amphoteric crosslinked polymer, which is a compound obtained by coordinating the acid-base amphoteric crosslinked polymer with a noble metal salt methanol solution and then reducing the coordination compound by sodium borohydride; the acid-base amphoteric crosslinked polymer is a crosslinked copolymer of divinylbenzene, vinyl heterocyclic monomers and acrylic monomers. The catalyst has high catalytic efficiency, does not need any other reaction auxiliary agents such as oxidant or inorganic base except oxygen, and the like, has adjustable reaction conversion rate and selectivity, can be recycled by centrifugation or filtration after the reaction is finished, is green and environment-friendly, and better meets the requirements of sustainable development.

Description

Amphoteric cross-linked polymer supported noble metal catalyst and preparation and alcohol oxidation method

technical field

The invention relates to the technical field of catalyst design, in particular to an acid-base amphoteric cross-linked polymer-supported noble metal nanoparticle catalyst and a preparation method thereof, and an acid-base amphoteric cross-linked polymer-supported noble metal nanoparticle catalyst catalyzed in the selective oxidation reaction of alcohol Applications.

Background technique

The catalytic oxidation of alcohols is an important functional group conversion reaction in organic synthesis. It is widely used in the manufacture of various intermediates and fine chemicals, and is of great significance in scientific research and chemical production. However, traditional alcohol oxidation reactions require the use of a stoichiometric amount of inorganic oxidants while using a large amount of organic solvents. These reagents can effectively oxidize alcohols to target products and also generate a large number of harmful by-products. Oxygen widely exists in the air and is cheap. Oxygen is used as the oxidant, and the by-product is only water, so it is an ideal oxidant for green environmental protection. At present, it has been realized that the nanoparticles of noble metals (platinum, gold and palladium, etc.) are used as catalysts to catalyze oxygen. Oxidation of alcohols. However, when oxygen is used as the oxidant, a large amount of inorganic base needs to be added as an auxiliary to improve the conversion rate of the reaction. In addition, the oxidation reaction of alcohols is poorly controllable, and aldehydes are easily oxidized to acids and esters. Therefore, in today's increasingly attention to green chemistry, no matter from the needs of environmental protection and sustainable development, or from the point of view of improving economic benefits, it is urgent to develop the replacement of traditional oxidation systems with oxygen, without the use of external solvents, without the use of A green and efficient oxidation reaction system with additives such as inorganic bases and a highly efficient catalyst with controllable selectivity, easy operation and easy separation.

Supported nano-precious metal catalyst is a good choice. Its carrier mainly plays the following three functions: 1) stabilizing and dispersing nano-precious metal to avoid agglomeration; 2) interacting with nano-precious metal to affect the charge state and morphology of nano-precious metal; 3. ) modulates the microscopic environment around the nano-precious metal, such as acidity and alkalinity, hydrophilicity and hydrophobicity, etc., which in turn affects the substrate conversion efficiency and target product selectivity. So far, many carriers have been used to support nano-precious metals, mainly including carbon materials, oxides and organic polymers.

However, the most widely studied inorganic supports such as carbon materials and oxide supports are low in price, but their types are limited, and their properties such as acidity, alkalinity, lipophilicity and hydrophilicity can be adjusted in a narrow range. However, there are many kinds of organic polymer carriers and a wide range of choices, such as acidity and alkalinity, hydrophilicity and hydrophobicity, and spatial cross-linking structure. By finely tuning these properties, the size of nano-precious metals and their surrounding microenvironment can be effectively regulated, thereby significantly enhancing the catalytic conversion efficiency of substrates and the selectivity of target products. However, there are few studies on the preparation and catalytic application of organic polymer-supported nano-precious metal catalysts. The cross-linked polymer-based carrier can provide a spatial network structure, which can well fix the noble metal nanoparticles while being easy to separate, and avoid the loss of noble metal nanoparticles to a large extent.

Aiming at the characteristics of alcohol selective oxidation reaction, the invention designs and synthesizes a nano-precious metal catalyst supported by an acid-base amphoteric cross-linked polymer. The oxidation of alcohol is catalyzed by acid-base synergy to achieve higher catalytic efficiency and selectivity, and the catalyst is easy to separate after the reaction is completed. And can be recycled.

SUMMARY OF THE INVENTION

The invention provides an acid-base amphoteric cross-linked polymer-supported noble metal nanoparticle catalyst with high catalytic efficiency and easy recovery.

The invention also provides a preparation method of an acid-base amphoteric crosslinked polymer-supported noble metal nanoparticle catalyst, which is simple to operate, easy to control, and suitable for industrial production.

The invention also provides an application method of the acid-base amphoteric cross-linked polymer-supported noble metal nanoparticle catalyst in catalyzing the aldol condensation reaction, and the catalyst in the method can be recovered and reused.

An acid-base amphoteric cross-linked polymer-supported noble metal nanoparticle catalyst is a compound obtained by reducing sodium borohydride after the acid-base amphoteric cross-linked polymer is coordinated with a noble metal salt methanol solution;

The acid-base amphoteric cross-linked polymer described in the present invention is a cross-linked copolymer of divinyl benzene, vinyl heterocyclic monomers and acrylic monomers, which can be synthesized according to the prior art methods, such as those described in the literature. loading method (Homogeneous-like solid base catalysts based on pyridine-functionalized swelling porouspolymers. Catalysis Communications, 2011, 11, 1212-1217.).

The divinylbenzene monomer is the compound represented by the formula (I) (DVB) structural formula, and the nitrogen-containing vinyl heterocyclic monomer is of formula (II) (VI), (III) (VP) or ( IV) (NVP) the compound represented by the structural formula:

In formula (I), R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are the same or different, R ₁ is hydrogen, an alkyl group or vinyl group having 1 to 4 carbon atoms, and R ₂ is hydrogen, carbon atom alkyl or vinyl having 1 to 4, R ₃ is hydrogen, alkyl or vinyl having 1 to 4 carbon atoms, R ₄ is hydrogen, alkyl or vinyl having 1 to 4 carbon atoms, R ₅ is hydrogen, an alkyl group having 1 to 4 carbon atoms or a vinyl group, R ₁ , R ₂ , R ₃ , R ₄ and R ₅ are the same or different, and at least one of them is a vinyl group;

In formula (II), R ₆ is hydrogen, an alkyl group having 1 to 4 carbon atoms or a vinyl group, R ₇ is hydrogen, an alkyl group or vinyl group having a carbon number of 1 to 4, and R ₈ is hydrogen, carbon atoms Alkyl or vinyl having 1 to 4 atoms, R ₉ is hydrogen, alkyl or vinyl having 1 to 4 carbon atoms, R ₆ , R ₇ , R ₈ and R ₉ are the same or different, and at least one is vinyl;

In formula (III), R ₁₀ is hydrogen, an alkyl group having 1 to 4 carbon atoms or a vinyl group, R ₁₁ is hydrogen, an alkyl group or vinyl group having a carbon number of 1 to 4, and R ₁₂ is hydrogen, carbon atoms Alkyl or vinyl having 1 to 4 atoms, R ₁₃ is hydrogen, alkyl or vinyl having 1 to 4 carbon atoms, R ₁₄ is hydrogen, alkyl or vinyl having 1 to 4 carbon atoms , R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ and R ₁₄ are the same or different, and at least one of them is vinyl;

In formula (IV), R ₁₅ is hydrogen, an alkyl group having 1 to 4 carbon atoms or a vinyl group, R ₁₆ is hydrogen, an alkyl group or vinyl group having a carbon number of 1 to 4, and R ₁₇ is hydrogen, carbon atoms Alkyl or vinyl having 1 to 4 atoms, R ₁₈ is hydrogen, alkyl or vinyl having 1 to 4 carbon atoms, R ₁₅ , R ₁₆ , R ₁₇ and R ₁₈ are the same or different, and at least one is vinyl;

In formula (V), R ₁₉ is hydrogen or methyl;

The molar ratio of divinylbenzene monomers to nitrogen-containing vinyl heterocyclic monomers and acrylic monomers in the acid-base amphoteric cross-linked polymer is 1-10:1:0.1-10, preferably 3 ~5:1:1.

The precious metal salt solution is a methanol solution of gold trichloride, tetrachloroauric acid, chloroplatinic acid, sodium hexachloroplatinate or ammonium tetrachloropalladate;

The mass ratio of the noble metal salt to the polymer is 0.1-20:100, preferably 5-20:100.

The specific preparation method of the nitrogen-containing cross-linked polymer-supported gold nanoparticle catalyst is as follows: according to the mass ratio of the noble metal salt to the acid-base amphoteric cross-linked polymer, the acid-base amphoteric cross-linked polymer is immersed in methanol containing the noble metal salt. The solution is vigorously stirred for 6 to 24 hours, and the solid obtained by the coordination reaction between the noble metal ion and nitrogen in the acid-base amphoteric cross-linked polymer is immersed in the methanol solution of the reducing agent prepared according to the molar ratio of the noble metal salt and the reducing agent. and vigorously stirring for 2 to 12 hours to obtain an acid-base amphoteric cross-linked polymer-supported noble metal nanoparticle catalyst.

The mass fraction of the noble metal nanoparticles in the catalyst is 0.5-20%, preferably 1-10%.

The size of the noble metal nanoparticles ranges from 0.5 to 12 nm, preferably from 2 to 8 nm.

A method for selective oxidation of alcohol, the specific scheme comprises adding a catalyst to liquid alcohol to carry out the oxidation reaction of alcohols in an oxygen atmosphere.

The temperature of the oxidation reaction is 20˜100° C., and the time of the oxidation reaction is 2 hours˜30 hours.

Described alcohol adopts benzyl alcohol, o-methyl benzyl alcohol, m-methyl benzyl alcohol, p-methyl benzyl alcohol, o-ethyl benzyl alcohol, m-ethyl benzyl alcohol, p-ethyl benzyl alcohol, phenethyl alcohol, o-methyl benzyl alcohol. Phenyl alcohol, m-methyl phenethyl alcohol, p-methyl phenethyl alcohol, o-ethyl phenethyl alcohol, m-ethyl phenethyl alcohol, p-ethyl phenethyl alcohol, o-tert-butyl benzyl alcohol, m-tert-butyl benzyl alcohol, p-tert-butyl alcohol Benzyl alcohol, o-tert-butyl phenethyl alcohol, m-tert-butyl phenethyl alcohol, p-tert-butyl phenethyl alcohol, o-nitrobenzyl alcohol, m-nitrobenzyl alcohol, p-nitrobenzyl alcohol, o-nitrophenethyl alcohol, m-nitrobenzyl alcohol One of nitrophenethyl alcohol, p-nitrophenethyl alcohol and 1-octanol.

The molar ratio of the alcohol to the precious metal in the catalyst is 500-100,000:1.

The raw materials and reagents described in the present invention can all be commercially available products.

Compared with the prior art, the present invention has the following remarkable progress:

The catalyst of the invention combines the characteristics of noble metal nanoparticles and acid-base amphoteric cross-linked polymers; the size of noble metal nanoparticles is controllable; the catalyst has acidity and alkalinity because it has carboxyl group and imidazole group at the same time, so that acid-base synergistic reaction can be achieved; The acid-base amphoteric cross-linked polymer has a spatial network structure. After the noble metal ions are complexed with nitrogen, they can be fixed in the network while being reduced. It can be adjusted by adjusting the nitrogen content, cross-linking degree and the amount of noble metal salt. The loading amount and size of the precious metal in the catalyst; after the acid-base amphoteric cross-linked polymer supports the precious metal nanoparticles, it can only swell but not dissolve, and after the catalytic reaction is completed, it can be recycled by simple filtration or centrifugation; The synthesis method does not use additional solvent, is more convenient and feasible, is green, environmentally friendly, safe and non-toxic, has broad development space and great market application value, and is more in line with the requirements of sustainable development.

The catalyst of the invention has high catalytic efficiency, does not need any other oxidant or inorganic base and other reaction aids except oxygen, and the reaction conversion rate and selectivity are adjustable. After the reaction is completed, the catalyst can be separated and recycled by centrifugation or filtration.

Detailed ways

Example 1 Preparation of acid-base amphoteric cross-linked polymer-supported nano-precious metal catalyst

In a three-necked flask, add divinylbenzene (DVB) (2.0g, 15mmol), vinylimidazole (VI) (0.483g, 5mmol), acrylic acid (AA) (0.360g, 5mmol), azobisisobutyronitrile (0.07g) and ethyl acetate (30ml) under nitrogen. The reaction was carried out at 100° C. for 24 hours without stirring. After the reaction, the solvent was dried to obtain 2.5 g of white powder, which was a copolymer of divinylbenzene, vinylimidazole and acrylic acid (PDVB-VI-AA).

200 mg of the above white powder was immersed in a methanol solution (10 mL) of AuCl ₃ (20 mg), vigorously stirred for 16 h, centrifuged, washed with methanol, put into a methanol solution (10 mL) of sodium borohydride (20 mg), vigorously stirred for 6 h, centrifuged, methanol Washing to obtain a nitrogen-containing acid-base amphoteric cross-linked polymer-supported nano-gold catalyst with a gold loading of 2.6% and a particle size of 3.5±1.0 nm.

Examples 2 to 7

Adopt the method of embodiment 1 to prepare acid-base amphoteric cross-linked polymer-supported nano-precious metal catalyst, the difference is that the mol ratio of DVB to VI and AA and the consumption of gold trichloride when synthesizing PDVB-VI are changed, as shown in Table 1:

Examples 8 to 9

The method of Example 1 was used to prepare the acid-base amphoteric cross-linked polymer supported nano-precious metal catalyst.

Examples 10 to 12

The acid-base amphoteric cross-linked polymer-supported nano-precious metal catalyst was prepared by the method of Example 1, except that the noble metal salt and the amount used to prepare the catalyst were changed, as shown in Table 3: Selective oxidation of alcohol in Example 13

In the jacketed reactor with stirring paddle, thermometer and gas inlet and outlet, benzyl alcohol (0.3g) and 54 mg of the catalyst prepared in Example 1 were fed with oxygen, and the temperature of the reactor was raised to 90 ° C after stirring evenly , under the stirring speed of 600rotor/min (revolution/min), the reaction was carried out for 16 hours. After the reaction, the catalyst was recovered by centrifugal separation, and the catalyst recovery rate was 97.6%. The reaction mixture was diluted with ethyl acetate, and the ethyl acetate solution was analyzed by gas chromatography to obtain benzyl alcohol conversion of 90.3%, product selectivity: benzaldehyde 80.1%, benzoic acid 13.2%, benzyl benzoate 6.7%.

Examples 14 to 19

According to the selective oxidation of alcohol by the method of Example 13, the difference is that the catalysts prepared in Examples 2 to 7 are respectively adopted, and the reaction results are shown in Table 4:

Examples 20 to 21

According to the selective oxidation of alcohol by the method of Example 13, the difference is that the catalysts prepared in Examples 8 to 9 are used respectively, and the reaction results are shown in Table 5:

Examples 22 to 24

According to the selective oxidation of alcohol by the method of Example 13, the difference is that the catalysts prepared in Examples 10 to 12 are used respectively, and the reaction results are shown in Table 6:

Table 1

Example serial number Amount of gold chloride (mg) DVB:VI:AA(mol) Gold loading (%) Particle size (nm) 2 20 3:1:1 4.2 3.4±1.2 3 40 3:1:2 7.8 4.5±1.1 4 10 10:3:2 1.7 2.8±1.1 5 20 2:1:1 2.9 3.0±0.9 6 10 6:1:1 6.4 3.2±1.0 7 20 10:3:5 7.8 4.2±1.2

Table 2

table 3

Table 4

table 5

Table 6

Example 25

Selective oxidation of alcohols according to the procedure of Example 13, except that n-octanol (0.27 g) was used instead of benzyl alcohol. The catalyst recovery rate was 96%, the conversion rate of benzyl alcohol was 60.3%, and the product selectivity was: n-octylaldehyde 30.2%, n-octanoic acid 57.5%, and octyl octyl ester 12.3%.

Example 26

Selective oxidation of alcohol according to the method of Example 13, except that the reaction temperature is 60°C and the reaction time is 24 hours. The catalyst recovery rate was 97%, the conversion rate of benzyl alcohol was 85.7%, and the product selectivity was: benzaldehyde 78.2%, benzoic acid 16.8%, benzyl benzoate 5.0%.

Example 27

Selective oxidation of alcohol according to the method of Example 13, except that the reaction temperature is 100°C and the reaction time is 12 hours. The catalyst recovery rate was 96.6%, the conversion rate of benzyl alcohol was 92.6%, and the product selectivity was: benzaldehyde 82%, benzoic acid 10.7%, benzyl benzoate 6.5%.

Example 28

Selective oxidation of alcohols according to the method of Example 13, except that Example 23 was used to recover the resulting catalyst. The conversion rate of benzyl alcohol was 91%, and the product selectivity was: benzaldehyde 85.8%, benzoic acid 7.8%, benzyl benzoate 6.8%.

Claims (9)

1. The amphoteric crosslinked polymer supported noble metal catalyst is characterized in that: the acid-base amphoteric crosslinked polymer supported noble metal catalyst is a compound obtained by coordinating the acid-base amphoteric crosslinked polymer with a soluble noble metal salt solution and then reducing the coordination compound by sodium borohydride;

the acid-base amphoteric crosslinked polymer is a crosslinked copolymer of a divinyl benzene monomer, a nitrogen-containing vinyl heterocyclic monomer and an acrylic monomer;

wherein the divinylbenzene monomer is a compound shown in a structural formula (I), the nitrogen-containing vinyl heterocyclic monomer is one or more than one of compounds shown in structural formulas (II), (III) or (IV), and the acrylic monomer is a compound shown in a structural formula (V):

in the formula (I), R₁Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₂Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₃Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₄Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₅Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁、R₂、R₃、R₄And R₅Any 2 or more of them are the same or different, and at least one is a vinyl group;

in the formula (II), R₆Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₇Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₈Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₉Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₆、R₇、R₈And R₉Any 2 or more of them are the same or different, and at least one is a vinyl group;

in the formula (III), R₁₀Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₁Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₂Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₃Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₄Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₀、R₁₁、R₁₂、R₁₃And R₁₄Any 2 or more of them are the same or different, and at least one is a vinyl group;

in the formula (IV), R₁₅Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₆Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₇Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₈Is hydrogen, alkyl or vinyl with 1 to 4 carbon atoms, R₁₅、R₁₆、R₁₇And R₁₈Any 2 or more of them are the same or different, and at least one is a vinyl group;

in the formula (V), R₁₉Is hydrogen or methyl.

2. The catalyst of claim 1, wherein: the molar ratio of the divinyl benzene monomer to the nitrogen-containing vinyl heterocyclic monomer to the acrylic monomer in the acid-base amphoteric crosslinked polymer is 1-10: 1: 0.1-10.

3. The catalyst of claim 1, wherein: the noble metal salt solution is methanol solution of one or more than two of gold trichloride, tetrachloroauric acid, chloroplatinic acid, sodium hexachloroplatinate or ammonium tetrachloropalladate.

4. The catalyst of claim 1, wherein: the mass ratio of the noble metal salt to the polymer is 0.1-20: 100.

5. A process for preparing a catalyst as claimed in any one of claims 1 to 4, comprising the steps of: according to the required mass ratio of the noble metal salt to the acid-base amphoteric crosslinked polymer of 0.1-20: 100, immersing the acid-base amphoteric crosslinked polymer into a methanol solution containing the noble metal salt, wherein the concentration of the methanol solution is 0.1-10 mg/mL, vigorously stirring the methanol solution for 6-24 hours, taking out a solid obtained by the coordination reaction of noble metal ions and nitrogen in the acid-base amphoteric crosslinked polymer, immersing the solid into a methanol solution of a reducing agent prepared according to the required molar ratio of the noble metal salt to the reducing agent, vigorously stirring the mixture for 2-12 hours, taking out the solid, and obtaining the acid-base amphoteric crosslinked polymer supported noble metal nanoparticle catalyst, wherein the particle size of the supported noble metal nanoparticles is 1-10 nm.

6. An alcohol oxidation method comprising adding a catalyst to a liquid alcohol to perform an alcohol oxidation reaction in an oxygen atmosphere, characterized in that: the catalyst is the amphoteric crosslinked polymer supported noble metal catalyst as described in any one of claims 1-5.

7. The alcohol oxidation process according to claim 6, wherein the temperature of the oxidation reaction is 20 to 100 ℃ and the time of the oxidation reaction is 2 to 30 hours.

8. The alcohol oxidation process according to claim 6, wherein said alcohol is one or more selected from the group consisting of benzyl alcohol, o-methyl benzyl alcohol, m-methyl benzyl alcohol, p-methyl benzyl alcohol, o-ethyl benzyl alcohol, m-ethyl benzyl alcohol, p-ethyl benzyl alcohol, phenethyl alcohol, o-methyl phenethyl alcohol, m-methyl phenethyl alcohol, p-methyl phenethyl alcohol, o-ethyl phenethyl alcohol, p-ethyl phenethyl alcohol, o-t-butyl benzyl alcohol, m-t-butyl benzyl alcohol, p-t-butyl benzyl alcohol, o-t-butyl phenethyl alcohol, m-t-butyl phenethyl alcohol, p-t-butyl phenethyl alcohol, o-nitrobenzyl alcohol, m-nitrobenzyl alcohol, p-nitrobenzyl alcohol, and 1-octanol.

9. The alcohol oxidation process of claim 6, wherein the molar ratio of alcohol to noble metal charge in the catalyst is from 500 to 100000: 1.