CN114602475B

CN114602475B - Hydrophobic nickel-carbon catalyst and preparation method and application thereof

Info

Publication number: CN114602475B
Application number: CN202210283386.6A
Authority: CN
Inventors: 曹景沛; 解金旋; 赵小燕; 李强; 江玮; 张创
Original assignee: China University of Mining and Technology CUMT
Current assignee: China University of Mining and Technology CUMT
Priority date: 2022-03-22
Filing date: 2022-03-22
Publication date: 2023-03-10
Anticipated expiration: 2042-03-22
Also published as: CN114602475A

Abstract

The invention discloses a hydrophobic nickel-carbon catalyst and a preparation method and application thereof, wherein hydrophilic active carbon, trimethylchlorosilane and cyclohexane are uniformly mixed, then the mixed solution is stirred for 8-20h at room temperature, and after the stirring is finished, vacuum drying is carried out to obtain hydrophobic active carbon; adding hydrophobic active carbon into a nickel salt water solution, and stirring and dispersing; then dipping the mixed solution in a vacuum chamber for 12-48h at the temperature; and then drying the sample, placing the dried catalyst in a pyrolysis tube, calcining for 1-4h at 450 ℃ in an inert atmosphere, and then reducing for 1-4h at 450 ℃ in a hydrogen atmosphere to obtain the hydrophobic nickel-carbon catalyst. Compared with the Ni/AC before modification, the modified catalyst can obviously inhibit the hydrolysis of diphenyl ether, the activity of the catalyst is not affected, the reaction process is simple, the C-O bond in the diphenyl ether can be directionally cracked, and a product with high added value is generated.

Description

Hydrophobic nickel-carbon catalyst and preparation method and application thereof

Technical Field

The invention relates to the field of preparation of nickel catalysts, and particularly relates to a hydrophobic nickel-carbon catalyst and a preparation method and application thereof.

Background

Lignin is an extremely abundant biomass resource that has the potential to replace coal or crude oil as a source of various chemical products. Lignin is a natural polymer of methoxyphenylpropane, and due to its high aromatic content, lignin can be used as a sustainable chemical feedstock for the production of high value-added aromatics, hydrocarbon fuels, and other intermediates. By the directional cleavage of the C-O bonds in lignin, a number of valuable aromatics and liquid fuels can be obtained. The lignin contains a large number of aryl ether C-O bonds, mainly alpha-O-4, beta-O-4 and 4-O-5 bonds. Among them, the 4-O-5 bond is the strongest C-O bond in lignin, and therefore, the selective cleavage of the C-O bond in the 4-O-5 bond is of great significance for the depolymerization of lignin. In which extensive studies have been conducted on lignin model compounds (diphenyl ether) due to the complexity of the lignin structure. The diphenyl ether has a symmetrical structure and is easy to generate hydrolysis reaction, so that the carrier and the catalyst thereof can be subjected to directional hydrogenolysis without hydrolysis reaction through modification, thereby directionally generating the required target product and simplifying the mechanism process of the reaction.

In the directional hydrogenolysis process of diphenyl ether, activated Carbon (AC) is often selected as a catalyst carrier to prepare a corresponding metal catalyst due to large specific surface area and high activity, but some AC has a pore structure and hydrophilic properties, and the prepared nickel-carbon catalyst is easy to cause partial diphenyl ether to generate hydrolysis reaction, so that the reaction path is complicated. Therefore, if the diphenyl ether can be subjected to a directional cleavage reaction under mild conditions, both a highly active catalyst and a directional cleavage thereof should be selected.

Disclosure of Invention

The invention aims to provide a preparation method of hydrophobic nickel-carbon activated carbon, which is used for carrying out hydrophobic modification on hydrophilic activated carbon.

The second purpose of the invention is to provide the hydrophobic nickel-carbon catalyst prepared by the preparation method.

The invention also aims to provide the application of the hydrophobic nickel-carbon catalyst in the aspect of directionally catalyzing and hydrogenolyzing diphenyl ether.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

in a first aspect, the invention provides a preparation method of hydrophobic nickel-carbon activated carbon, which comprises the following steps:

(1) Uniformly mixing hydrophilic activated carbon, trimethylchlorosilane (TMCS) and solvent cyclohexane, stirring the mixed solution at room temperature for 8-20h, and drying the mixed solution in a vacuum drying oven at normal temperature for 10-36h after stirring to obtain hydrophobic activated carbon; wherein the mass volume ratio of the hydrophilic active carbon to the trimethylchlorosilane is 0.2g:1mL;

(2) Adding the hydrophobic activated carbon prepared in the step (1) into a nickel salt aqueous solution, and stirring and dispersing; then the mixed solution is dipped in vacuum for 12 to 48 hours at room temperature; and then drying the sample, placing the dried catalyst in a pyrolysis tube, calcining for 1-4h at 450 ℃ in an inert atmosphere, and then reducing for 1-4h at 450 ℃ in a hydrogen atmosphere to obtain the hydrophobic nickel-carbon catalyst.

Preferably, the activated carbon in step (1) is in the form of powder.

Preferably, the nickel salt in step (2) is selected from one or more of nickel nitrate hexahydrate, nickel chloride hexahydrate, basic nickel carbonate or nickel acetate.

In a second aspect, the invention provides a hydrophobic nickel-carbon catalyst prepared by the preparation method.

Preferably, the loading of nickel in the hydrophobic nickel-carbon catalyst is 10% by weight.

In a third aspect, the invention provides an application of the hydrophobic nickel-carbon catalyst in the aspect of directionally catalyzing and hydrogenolyzing diphenyl ether.

The specific application steps comprise: putting reactant diphenyl ether, hydrophobic nickel-carbon catalyst and solvent into a reaction kettle. After sealing, residual air is removed by introducing hydrogen for 3 times, and then hydrogen with a certain pressure (1.0-2.0 MPa) is introduced into the reaction kettle. Subsequently, the reaction vessel was heated to the desired reaction temperature (160-180 ℃) at room temperature and stirred for a period of time (110-120 min). After the reaction is finished, the reaction kettle is naturally cooled to room temperature and decompressed. The liquid after the reaction was filtered, and the collected liquid was analyzed for liquid products by a gas chromatography-mass spectrometer (GC-MS) and a Gas Chromatograph (GC).

Preferably, the hydrogen pressure is 1.0MPa, the reaction temperature is 160 ℃, and the reaction time is 120min.

Preferably, the organic solvent is isopropanol.

Compared with the prior art, the invention has the following beneficial effects:

compared with the Ni/AC before modification, the modified Ni/1mLTMCS-AC can obviously inhibit the hydrolysis of diphenyl ether, the activity of the catalyst is not affected, the reaction process is simple, the C-O bond in the diphenyl ether can be directionally cracked, a product with high added value is generated, and the modification method of the catalyst for directionally cracking the C-O bond is provided.

Drawings

FIG. 1 is an IR spectrum of 1mL of TMCS-AC as a support obtained in example 1 of the present invention;

FIG. 2 is an XPS spectrum of 1mL of TMCS-AC as a support prepared in example 1 of the present invention;

FIG. 3 is an XRD pattern of Ni/1mL TMCS-AC catalyst prepared in example 1 of the present invention;

FIG. 4 is a reaction pathway diagram of Ni/1mL TMCS-AC catalyzed diphenyl ether conversion;

FIG. 5 is a graph of the effect of reaction temperature on the catalytic hydrogenolysis of diphenyl ether;

FIG. 6 is the effect of reaction pressure on the catalytic hydrogenolysis of diphenyl ether;

FIG. 7 is a graph of the effect of reaction time on the catalytic hydrogenolysis of diphenyl ether.

Detailed Description

The invention is described in further detail below with reference to the figures and specific examples.

The prepared ACs that are hydrophobically modified are named in the following way: x mL TMCS-AC (X is the volume of trimethylchlorosilane).

Example 1: preparation of catalyst Ni/1mL TMCS-AC

1. Preparation of 1mL of Carrier TMCS-AC

0.2g of hydrophilic powdery AC, 1mL of Trimethylchlorosilane (TMCS) and 10mL of solvent cyclohexane are selected and uniformly mixed, and then the mixed solution is stirred for 10 hours at room temperature, wherein the rotating speed is 200r/min. After stirring, the mixed solution is dried in a vacuum drying oven at normal temperature for 12 hours to obtain hydrophobic 1mL TMCS-AC.

2. Impregnation method for preparing nickel-carbon catalyst

0.11g of nickel nitrate was placed in a beaker, and 0.5mL of deionized water was added to completely dissolve it. 0.2g of 1mL of TMCS-AC-2 obtained above was added to the above ionic solution, and stirred with a glass rod for 5min to ensure high dispersion. The mixed solution was then immersed for 24h at vacuum chamber temperature to ensure high dispersion of the metal precursor on the support. The sample was then dried in an oven at 110 ℃ for 4h. The dried catalyst is placed in a pyrolysis tube, the argon (Ar) is used as protective gas, the flow rate is 60mL/min, the calcination is carried out for 1H at the temperature of 450 ℃, and then the hydrogen (H) with the flow rate of 60mL/min is carried out ₂ ) Reducing for 1h under the condition of atmosphere and temperature of 450 ℃ to obtain the Ni/1mLTMCS-AC catalyst. The loading was 10% by weight.

Example 2: preparation of catalyst Ni/0.5mL TMCS-AC

The preparation process was substantially the same as in example 1, except that TMCS was added in an amount of 0.5mL.

Example 3: preparation of catalyst Ni/1.5mL TMCS-AC

The preparation process was substantially the same as in example 1, except that TMCS was added in an amount of 1.5mL.

Comparative example: preparation of catalyst Ni/AC

The same procedure for the preparation of the catalyst as in the second part of example 1 was followed, except that hydrophilic AC (i.e., AC before modification) was used.

TABLE 1 physical Properties of Nickel-carbon catalysts and Supports

^a The total specific surface area is calculated by the BET formula.

^b At a relative pressure P/P ₀ Measurement of Total porosity at =0.99And (4) accumulating.

^c The specific surface area and volume of the micropores were calculated by the t method.

^d The total specific surface area and the micropore surface area and the difference between the total pore volume and the micropore volume.

The physical properties of the support and the catalyst are shown in table 1. The specific surface area of the AC before modification was 1731m ² The specific surface area and micropore volume of 1mL TMCS-AC after modification decreased slightly, probably due to the addition of TMCS, which caused it to plug a portion of the micropores at the surface, indicating that TMCS was successfully added to the surface of the AC support. When the nickel metal is impregnated into the carrier, the specific surface areas of Ni/AC and Ni/1mL of TMCS-AC are reduced, which shows that the nickel can be loaded into the pore channels of the carrier, generally speaking, the physical property difference between the carrier and the catalyst before and after modification is not large, the hydrophilicity and hydrophobicity of the carrier are only changed after the TMCS is added, and the activity of the catalyst is not greatly influenced.

FIG. 1 is an IR spectrum of AC and 1ml LTMCS-AC as a support prepared in example 1. The principle of AC hydrophobic modification is that methylation reaction occurs on the surface, and the principle is shown in formula 1, wherein-OH group on the surface of AC reacts with TMCS to generate-O-Si (CH) ₃ ) ₃ And HCl, rendering the AC surface hydrophobic. The IR spectra before and after modification, 3690cm- ¹ The peak appears due to the stretching vibration absorption of-OH bond, 3200cm- ¹ The vibration peak of-CH is arranged on the left and the right. Wherein the peaks marked in the figure are the peaks which are more marked after modification. 2917cm- ¹ And 2843cm- ¹ Is represented by-CH ₃ This indicates that the methyl group successfully entered the AC surface after TMCS modification, rendering it hydrophobic. 839cm- ¹ Is of Si-CH ₃ The Si group is also incorporated into the AC surface, 616cm- ¹ As an absorption peak of Si-Cl, the peak intensity of Si-Cl was small and almost absent, indicating that Cl groups formed HCl, which was volatilized into the air, and almost absent on the AC surface.

-OH+(CH ₃ ) ₃ SiCl＝-O-Si(CH ₃ ) ₃ +HCl (1)

FIG. 2 is an XPS spectrum of 1mL of TMCS-AC as a support obtained in example 1. It can be seen from the figure that elemental silicon and very small amounts of chlorine were present on the surface of 1mL of TMCS-AC after modification, which further indicates that the addition of TMCS was successful on the support surface.

FIG. 3 is an XRD pattern of 1mL of TMCS-AC as a support and Ni as a catalyst per 1mL of TMCS-AC as prepared in example 1. As can be seen from the figure, the modified 1mL TMCS-AC carrier has no obvious characteristic peak as the common carbon carrier, and the 111, 200 and 220 crystal faces of the metallic nickel are obviously observed after the metallic nickel is added, which indicates that the nickel elementary crystals are successfully formed in the Ni/1mL LTMCS-AC.

Example 4: oriented catalytic hydrogenolysis application of diphenyl ether

100mg of diphenyl ether (DPE), 50mg of catalyst and 20mL of isopropanol were placed in a 100mL stainless steel autoclave and sealed. Then, the reaction vessel was purged with hydrogen three times to remove excess air, and hydrogen (1 MPa) was charged under a certain pressure. The temperature was set to the desired reaction temperature (160 ℃) and held at 800rpm for a certain time (120 min). After the reaction is finished, the reactor is naturally cooled to room temperature and decompressed. The catalyst and the liquid product were separated with a filter, and the liquid product was analyzed by a gas chromatography-mass spectrometer (GC-MS) and a Gas Chromatograph (GC).

TABLE 2 Effect of different nickel-carbon catalysts on DPE catalytic conversion

Reaction conditions are as follows: 100mg DPE,50mg Nickel-carbon catalyst, 20mL isopropanol, 160 ℃,1MPa H ₂ ，2h.

The effect of different nickel carbon catalysts on the catalytic conversion of DPE is listed in table 2. For conventional Ni/AC catalysts, DPE goes through three reaction paths: (1) 61.8 percent of DPE directly undergoes C-O bond cracking to generate benzene and phenol, and then is hydrogenated to generate cyclohexane and cyclohexanol; (2) DPE, which is 34.1%, is directly hydrolyzed to phenol, which is then hydrogenated to cyclohexanol; (3) is 4.1% of DPE direct aromatic ring hydrogenation to cyclohexyl ether and dicyclohexyl ether. For Ni/1mL TMCS-AC after hydrophobic modification, no hydrolysis reaction of DPE occurs when DPE is catalytically converted, and only the two reaction paths (1) and (3) are undergone: carrying out catalytic hydrogenolysis reaction on 91.8% of DPE directly to generate benzene, phenol, cyclohexane and cyclohexanol; 8.2% of the DPE direct aromatic ring was hydrogenated to cyclohexyl ether and dicyclohexyl ether, the reaction path is shown in FIG. 4. Wherein the selectivity of the hydrogenolysis of Ni/1mLTMCS-AC is far larger than that of Ni/AC, and the conversion rate of the two catalysts to DPE is not obviously different. The modified catalyst can inhibit the hydrolysis reaction of DPE, so that the DPE is directionally cracked to generate a target product, and the site selectivity control of the catalyst to generate the target product provides a direction. Then, the influence of the amount of TMCS added on the catalytic activity is further researched, and compared with Ni/1mL of TMCS-AC, the catalyst prepared by adding 0.5mL and 1.5mL of TMCS has obviously reduced activity on DPE cracking, and the selectivity of a target product is basically unchanged, which shows that the nickel-carbon catalyst modified by adding TMCS can effectively inhibit the hydrolysis reaction of DPE. In general, the conversion rate and the product selectivity of the Ni/1mL TMCS-AC catalyst on the selective hydrogenolysis of DPE are both high, and the directional breaking of C-O bonds in DPE is realized.

Example 5: effect of reaction temperature on Diphenyl Ether conversion

The reaction conditions are as follows: 100mg DPE,50mg Ni/1mL TMCS-AC,20mL isopropanol, 1MPa H ₂ ，2h.

The reaction temperature plays an important role in the directional catalytic cracking of DPE. Therefore, ni/1mL TMCS-AC with the best effect is selected, and the influence of temperature on the DPE catalytic hydrogenolysis is researched. As can be seen from FIG. 5, the conversion of DPE reached 27.3% at a reaction temperature of 140 ℃ and 97% with further increase of the reaction temperature to 160 ℃, indicating that increasing the temperature favors the cleavage of C-O bonds in DPE. The benzene and the phenol are gradually hydrogenated to generate the cyclohexane and the cyclohexanol with the increase of the temperature, and the selectivity of the hydrogenation product of the DPE aromatic ring is gradually reduced, so that the graph shows that the selectivity of the C-O cracking of the DPE is greater than the selectivity of the direct hydrogenation of the aromatic ring with the increase of the reaction temperature, and the increase of the temperature is favorable for the generation of the target product. When the temperature is further increased to 180 ℃, the conversion rate of DPE reaches 100%, phenol is completely converted into cyclohexanol because the hydrogenation capacity of phenol is higher than that of benzene, and the difference between the conversion rate of DPE and the selectivity of a target product and 160 ℃ is small, so that the optimal temperature for DPE hydrogenolysis is 160 ℃ in comprehensive consideration.

Example 6: effect of reaction time on Diphenyl Ether conversion

Reaction conditions are as follows: 100mg DPE,50mg Ni/1mL TMCS-AC,160 ℃,20mL isopropanol, 1MPa H ₂ .

Figure 6 shows the effect of reaction time on DPE catalytic hydrogenolysis. When the reaction temperature was 30min, the conversion of DPE was low at 20.7%, and gradually increased with further extension of the reaction time. With increasing time, the benzene and phenol are further hydrogenated to cyclohexane and cyclohexanol. When the reaction time was 120min, the conversion of DPE reached 97%, at which time DPE was almost completely converted, so 120min was selected as the optimum reaction time for this reaction.

Example 7: effect of Hydrogen pressure on Diphenyl Ether conversion

Reaction conditions are as follows: 100mg DPE,50mg Ni/1mL TMCS-AC,160 ℃,20mL isopropanol, 2h.

Figure 7 explores the effect of hydrogen pressure on DPE catalytic hydrogenolysis during the reaction. At a reaction pressure of 0.5MPa, the DPE conversion was 47.7%, and a large amount of benzene and phenol were also present in the reaction product. When the pressure of the hydrogen for reaction is increased to 1.0MPa, the conversion rate of DPE reaches 97%, and benzene and phenol are gradually hydrogenated to generate cyclohexane and cyclohexanol. When the pressure is further increased to 2.0MPa, DPE is completely converted, but at this time, a large amount of cyclohexyl ether is produced as a by-product in the product due to a high hydrogen pressure, and the by-product is increased with further increase in the reaction pressure, so that the most suitable hydrogen reaction pressure is 1.0MPa.

Claims

1. The application of the hydrophobic nickel-carbon catalyst in the aspect of directionally catalyzing and hydrogenolyzing diphenyl ether is characterized in that the preparation process of the hydrophobic nickel-carbon catalyst is as follows:

(1) Uniformly mixing hydrophilic activated carbon, trimethylchlorosilane and solvent cyclohexane, stirring the mixed solution at room temperature for 8-20h, and drying the mixed solution in a vacuum drying oven at room temperature for 10-36h after stirring to obtain hydrophobic activated carbon; wherein the mass volume ratio of the hydrophilic active carbon to the trimethylchlorosilane is 0.2g:1mL;

2. Use according to claim 1, wherein the activated carbon in step (1) is in powder form.

3. Use according to claim 1, wherein the nickel salt in step (2) is selected from one or more of nickel nitrate hexahydrate, nickel chloride hexahydrate, nickel hydroxycarbonate or nickel acetate.

4. The use according to claim 1, wherein the loading of nickel in the hydrophobic nickel-carbon catalyst is 10% wt.

5. The use according to claim 1, characterized in that the specific application steps comprise: putting reactants diphenyl ether, a hydrophobic nickel-carbon catalyst and an organic solvent into a reaction kettle; after sealing, removing residual air by introducing hydrogen for 3 times, and then introducing hydrogen with the pressure of 1.0-2.0MPa into the reaction kettle; then, heating the reaction kettle to 160-180 ℃ at room temperature, and stirring for reaction for 110-120min; after the reaction is finished, naturally cooling the reaction kettle to room temperature and releasing pressure; the liquid after the reaction was filtered, and the collected liquid was analyzed for liquid products by a gas chromatography-mass spectrometer and a gas chromatograph.

6. Use according to claim 5, wherein the hydrogen pressure is 1.0MPa, the reaction temperature is 160 ℃ and the reaction time is 120min.

7. Use according to claim 5, wherein the organic solvent is isopropanol.