CN113499785B - Magnetically-separable carbon-supported monatomic palladium catalyst and preparation method and application thereof - Google Patents

Magnetically-separable carbon-supported monatomic palladium catalyst and preparation method and application thereof Download PDF

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CN113499785B
CN113499785B CN202110471991.1A CN202110471991A CN113499785B CN 113499785 B CN113499785 B CN 113499785B CN 202110471991 A CN202110471991 A CN 202110471991A CN 113499785 B CN113499785 B CN 113499785B
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phenylacetylene
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CN113499785A (en
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刘洪阳
赵琳敏
黄飞
刁江勇
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Institute of Metal Research of CAS
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Abstract

The invention discloses a magnetically separable carbon-supported monatomic palladium catalyst, and a preparation method and application thereof, and belongs to the technical field of phenylacetylene selective hydrogenation catalysts. Firstly, preparing a carbon material with a nickel-coated graphene core-shell structure as a carrier, and loading palladium on a graphene shell layer in a single-atom form. The catalyst realizes high-efficiency selective hydrogenation to generate styrene under the condition of high conversion rate of phenylacetylene under mild conditions, the using temperature of the catalyst is 20-80 ℃, and the hydrogen pressure is 1-10 bar. Compared with the traditional Lindla catalyst and a commercial palladium-carbon catalyst, the magnetically-separable carbon-supported monatomic palladium catalyst disclosed by the invention can realize the efficient selective hydrogenation of phenylacetylene under a mild condition, can realize the recovery and cyclic utilization of the catalyst by utilizing an external magnetic field, and accords with the concepts of environmental protection, energy conservation and emission reduction.

Description

Magnetically-separable carbon-supported monatomic palladium catalyst, and preparation method and application thereof
Technical Field
The invention relates to the technical field of phenylacetylene selective hydrogenation catalysts, in particular to a magnetically separable carbon-supported monatomic palladium catalyst, and a preparation method and application thereof.
Background
Styrene is one of the important monomers in chemical production, and is mainly used for synthesizing polymers such as ABS resin, styrene-butadiene rubber, polystyrene and the like. The prior method for producing styrene mainly comprises ethylbenzene dehydrogenation, pyrolysis gasoline recovery, butadiene synthesis, methanol synthesis and the like. The ethylbenzene dehydrogenation method is generally adopted in industry, but the method has higher production cost due to higher energy consumption and water resource consumption, and the market demand is difficult to meet only by ethylbenzene dehydrogenation. The pyrolysis gasoline accounts for about 60-70% of the ethylene production energy, the processing cost of extracting and recovering styrene by utilizing the C8C9 fraction is only half of that of styrene prepared by ethylbenzene dehydrogenation, so that the preparation of styrene from the C8C9 fraction of the pyrolysis gasoline is the most competitive process after the production scale is achieved with relatively low cost and low investment in the conventional styrene production technology. The most common process for recovering styrene from pyrolysis gasoline is extractive distillation. However, the chemical structures of phenylacetylene and styrene are similar, and the interaction between the phenylacetylene and styrene and an extraction solvent is also similar, so that phenylacetylene and styrene cannot be effectively separated by extractive distillation. However, the presence of phenylacetylene has a great influence on the product quality of styrene, and it is industrially desirable to eliminate the impurity phenylacetylene by selective hydrogenation of phenylacetylene to styrene in the presence of a large amount of styrene. Therefore, the development of a phenylacetylene selective hydrogenation catalyst with both high conversion rate and high selectivity is the key of a method for preparing styrene from pyrolysis gasoline.
Compared with homogeneous catalysts, heterogeneous catalysts show wider application prospects due to better separation and recovery characteristics. The catalysts commonly used in industry today for the hydrogenation of acetylenes are lindlar, raney nickel, commercial palladium on carbon catalysts. However, the catalysts have low catalytic activity and poor styrene selectivity, and industrial phenylacetylene selective hydrogenation reaction conditions are harsh, so that competitive adsorption exists due to the existence of a large amount of olefin, and the reaction pressure is as high as 1.5-3.5 MPa. Therefore, it is very important to develop a catalyst for preparing styrene by high-efficiency selective hydrogenation of phenylacetylene under mild conditions.
With the introduction of the concept of single atom, single atom catalysts are increasingly applied to various reactions and show excellent catalytic activity. For the supported noble metal catalyst, the noble metal is distributed on the surface of the carrier in a single atom form, so that the atom utilization rate is 100 percent, and the preparation cost of the catalyst is reduced. Therefore, the invention tries to develop the monoatomic palladium catalyst for the phenylacetylene selective hydrogenation reaction.
Disclosure of Invention
The invention aims to provide a magnetically-separable carbon-supported monatomic palladium catalyst, and a preparation method and application thereof. The prepared magnetically separable monatomic palladium catalyst is applied to the selective hydrogenation of phenylacetylene to prepare styrene so as to realize the efficient selective hydrogenation of phenylacetylene to prepare styrene under mild conditions, and an external magnetic field can be used for separating and recovering the catalyst.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a magnetically-separable carbon-supported monatomic palladium catalyst takes palladium as an active material, a nickel-coated graphene composite material as a carrier, the palladium is distributed on the nickel-coated graphene composite material carrier in a monatomic manner, and the palladium and carbon atoms on graphene defects form bonds.
The loading amount of palladium in the catalyst is 0.01-0.2 wt.%.
The preparation method of the magnetically separable monatomic palladium catalyst comprises the following steps:
(1) preparing a magnetic nickel-coated graphene composite material by using nickel hydroxide and citric acid monohydrate as raw materials;
(2) loading palladium species on the surface of the nickel-coated graphene composite material by a deposition precipitation method to obtain a magnetic palladium-based nickel-coated graphene composite material catalyst precursor;
(3) and (2) placing the magnetic palladium-based nickel-coated graphene composite catalyst precursor in a quartz tube, and carrying out reduction treatment in a hydrogen atmosphere to obtain the magnetically separable carbon-supported monatomic palladium catalyst.
The preparation process of the nickel-coated graphene composite material carrier in the step (1) is as follows: preparing a precursor by using nickel hydroxide and citric acid monohydrate, and performing high-temperature pyrolysis, wherein the mass ratio of the nickel hydroxide to the citric acid monohydrate is 1 (1-10), and the preparation method comprises the following specific steps: putting nickel hydroxide and citric acid monohydrate in a certain substance amount ratio into an oil bath in water, and stirring until the mixture is uniform to obtain a nickel citrate aqueous solution; after drying, putting the nickel citrate complex into a quartz boat for high-temperature pyrolysis carbonization treatment, wherein the high-temperature pyrolysis carbonization treatment process comprises the following steps: and (3) placing the nickel citrate raw material in an inert atmosphere of 500-900 ℃ and 30-80 ml/min for treatment, wherein the heating rate is 0.5-20 ℃/min, preferably 1-10 ℃/min, and the treatment time is 1-6 h, so as to obtain the magnetic nickel-graphene composite material. Then carrying out acid washing treatment on the obtained carbon material, wherein the treatment process comprises the following steps: and (3) using excessive hydrochloric acid for pickling for 12-24 h, carrying out acid pickling at the temperature of 20-80 ℃, carrying out suction filtration after pickling, cleaning with deionized water and absolute ethyl alcohol, and drying in a vacuum drying oven at the temperature of 60 ℃ for 12-24 h to obtain the magnetic nickel-coated graphene composite material carbon carrier.
In the step (2), the deposition precipitation method comprises the following steps: and (2) putting 200mg of the magnetic nickel-coated graphene composite material carrier obtained in the step (1) into a 100ml round-bottom flask, adding 30ml of deionized water, adjusting the pH to be alkaline under the condition of 100 ℃ oil bath, calculating the dosage of palladium nitrate according to the loading amount of palladium in the catalyst, adjusting the required amount of palladium nitrate solution to be neutral, dropwise adding the palladium nitrate solution into the carrier solution in the flask, and stirring for 1 hour. Standing and cooling to room temperature, carrying out vacuum drying for 12-24 h at 60 ℃ after suction filtration, and obtaining the magnetically separable carbon-supported monatomic palladium catalyst precursor.
In the step (3), the reduction process is as follows: reducing in a hydrogen atmosphere at the temperature of 100-200 ℃ for 1-3 h; and after reduction treatment, reducing the argon flow of 10-30 ml/min to room temperature to obtain the magnetically separable carbon-supported monatomic palladium catalyst.
The magnetically separable carbon-supported monatomic palladium catalyst is used as a catalyst for the phenylacetylene selective hydrogenation reaction. In the selective hydrogenation reaction process of phenylacetylene, a reactant is phenylacetylene, a solvent is ethanol, and a hydrogen source is hydrogen, wherein the ratio of the catalyst to the phenylacetylene is (25-40) mg: 1.85mmol, wherein the ratio of phenylacetylene to solvent is (1-5) mmol: (5-50) ml, and the using temperature of the catalyst is 20-80 ℃; the hydrogen pressure is 1-10 bar; the reaction time is 0.1-5 h. The catalyst has good activity and stability in the using process.
The invention has the following advantages and beneficial effects:
1. the carrier material used by the catalyst is a nickel-coated graphene composite material, and the surface of the carrier material has abundant defects and oxygen-containing functional groups, so that palladium atoms are anchored on the surface of the carrier through strong interaction between metal and the carrier. In addition, the active material used in the invention is palladium, and the palladium is loaded on the surface of the carrier in a single atom form, so that the atom utilization rate is improved, and the catalyst can realize the efficient selective hydrogenation of phenylacetylene under low load. In addition, because the carrier contains nickel particles, and nickel belongs to ferromagnetic metal, the carrier has certain magnetism, and the catalyst can be easily separated from the reaction solution through an external magnetic field to realize the recycling of the catalyst.
2. When the catalyst is used, the catalytic activity is good under mild conditions. Calculated by unit mass of noble metal palladium, the conversion rate of phenylacetylene at the initial reaction can reach 40.4 mol/(g.h), and the selectivity of styrene at the complete conversion can reach 93 percent.
3. The magnetically separable carbon-supported monatomic palladium catalyst provided by the invention can obtain higher phenylacetylene selective hydrogenation reaction activity under mild conditions, is far lower than the reaction pressure of a traditional industrial device, and is beneficial to improving the production efficiency.
4. The catalyst has no pollution to the environment, is easy and convenient to recover, and is environment-friendly and efficient.
Drawings
FIG. 1 is a magnetically separable schematic view of a catalyst support of the present invention.
FIG. 2 is a HAADF-STEM diagram of the catalyst of the present invention.
FIG. 3 is a graph showing the catalytic activity of the catalyst of the present invention.
FIG. 4 is a schematic diagram of magnetic separation and recovery before and after reaction of the catalyst of the present invention.
FIG. 5 is a graph showing stability tests of the catalyst of the present invention.
Detailed Description
The invention is described in detail below with reference to the accompanying drawings and examples.
Example 1:
the preparation process of the catalyst in this example is as follows:
the method for preparing the precursor solution by utilizing the nickel hydroxide and the citric acid monohydrate comprises the following specific preparation processes: putting nickel hydroxide and citric acid monohydrate into water according to the mass ratio of 1:2, and stirring the mixture in an oil bath at the temperature of 80 ℃ until the mixture is uniform to obtain a nickel citrate aqueous solution; and after drying, putting the nickel citrate complex into a quartz boat, and performing high-temperature pyrolysis carbonization treatment at 800 ℃ in an inert atmosphere to obtain the magnetic nickel-graphene composite material. Then carrying out acid washing treatment on the obtained carbon material, wherein the treatment process comprises the following steps: and (3) pickling for 12 hours by using excessive hydrochloric acid, treating the carbon carrier at the temperature of 40 ℃, then performing suction filtration, cleaning the carbon carrier by using a large amount of deionized water and absolute ethyl alcohol, and drying the carbon carrier for 12 hours in a vacuum drying oven at the temperature of 60 ℃ to obtain the magnetic nickel-coated graphene composite material carbon carrier. Putting 10mg of carrier into a sample tube, adding 2ml of absolute ethyl alcohol, placing a magnet on the outer wall of the sample tube after ultrasonic dispersion is uniform, standing and timing by a stopwatch to obtain the magnetic carrier in the solution for 10s, namely effectively separating the magnetic carrier from the solvent ethanol, as shown in figure 1. Putting 200mg of magnetic nano carbon carrier into a 100ml round bottom flask, adding 30ml of deionized water, adjusting the pH to be alkaline under the condition of 100 ℃ oil bath, calculating the dosage of palladium nitrate according to the loading amount of palladium in the catalyst, taking the required amount of palladium nitrate solution, adjusting the palladium nitrate solution to be neutral, dropwise adding the palladium nitrate solution into the carrier solution in the flask, and stirring for 1 h. Standing and cooling to room temperature, carrying out vacuum drying for 12h at 60 ℃ after suction filtration, and obtaining the magnetically separable carbon-supported monatomic palladium catalyst precursor. The mass of palladium was 0.1 wt.% of the magnetic nickel-coated graphene composite carrier. Then placing the obtained magnetically separable carbon-supported monatomic palladium catalyst precursor into a quartz tube, and reducing the catalyst precursor at 200 ℃ in a hydrogen atmosphere; after reduction treatment, the carbon-supported monatomic palladium catalyst which can be magnetically separated can be obtained after the argon gas flow of 10-30 ml/min is reduced to the room temperature, and the carbon-supported monatomic palladium catalyst is recorded as 0.1Pd/Ni @ G, and the spherical aberration electron microscope photo of the catalyst is shown in figure 2.
Example 2
This example is a test of the phenylacetylene selective hydrogenation catalytic performance of the catalyst prepared in example 1:
and (3) carrying out catalyst performance test by using a stainless steel high-pressure reaction kettle. Adding 25mg of 0.1Pd/Ni @ G into a 50ml quartz lining of a reaction kettle, adding 10ml ethanol solution containing 1.85mmol of phenylacetylene, placing the lining into a stainless steel reaction kettle, sealing, replacing air with argon for six times, heating to 30 ℃, replacing argon with hydrogen for five times, and adding H 2 The pressure is 0.2MPa, and the reaction time is 60 min. After the reaction, the composition of the reaction product was analyzed by gas chromatography to obtain phenylacetylene conversion of 96.4%, styrene selectivity of 96.9%, and total selectivity of other by-products of 3.1%.
Example 3
Following the procedure of example 2, the other conditions were unchanged except that the reaction time was 65min, and the composition of the reaction product after the reaction was analyzed by gas chromatography gave a phenylacetylene conversion of 100%, a styrene selectivity of 93%, and a total selectivity to other by-products of 7%.
With otherwise unchanged conditions, only the reaction times were varied, i.e. the activity and selectivity of the catalyst varied at different reaction times as shown in fig. 3.
Example 4
The procedure of example 2 was followed, except that the amount of the catalyst used was 30mg and the reaction time was 30 min. After the reaction, the composition of the reaction product is analyzed by gas chromatography, thus obtaining the phenylacetylene conversion rate of 50 percent and the styrene selectivity of 100 percent.
Example 5
The procedure of example 2 was followed, except that the amount of the catalyst used was 40mg and the reaction time was 30 min. After the reaction, the composition of the reaction product is analyzed by gas chromatography, so that the conversion rate of phenylacetylene is 65 percent, and the selectivity of styrene is 100 percent.
Example 6
The procedure of example 2 was followed, except that the reaction temperature was 40 ℃ and the reaction time was 10 min. After the reaction, the composition of the reaction product was analyzed by gas chromatography to obtain phenylacetylene conversion rate of 27.3% and styrene selectivity of 100%.
Example 7
The procedure of example 2 was followed, except that the reaction temperature was 50 ℃ and the reaction time was 10 min. After the reaction, the composition of the reaction product was analyzed by gas chromatography to obtain phenylacetylene conversion rate of 52.8% and styrene selectivity of 100%.
Example 8
The procedure of example 2 was followed, except that the reaction temperature was 60 ℃ and the reaction time was 5 min. After the reaction, the composition of the reaction product was analyzed by gas chromatography to obtain phenylacetylene conversion of 43.4% and styrene selectivity of 100%.
Example 9
The operation of example 2 was carried out under otherwise unchanged conditions, and the catalyst used alone was a recovered catalyst, and the cycle stability of the catalyst was tested. After each reaction, the catalyst recovery process comprises the following steps: standing the reaction solution to observe the phenomenon that the reaction solution of the catalyst adsorbed on the magnetons becomes clear (as shown in figure 4), pouring out the clear reaction solution, washing the catalyst with a large amount of water and absolute ethyl alcohol, pouring out the supernatant after standing, repeating the step three times, and drying the recovered catalyst in a vacuum drying oven at 60 ℃ for 6 hours. The reaction was then repeated for the cycling test following the procedure of example 2. Repeating the reaction for 5 times, and analyzing the composition of the reaction product by gas chromatography after each reaction to obtain a stability test chart of the catalyst, as shown in fig. 5.
Comparative example 1
The catalyst was prepared as in example 1 except that no noble metal monatomic palladium was supported, i.e., the pure support was used in the selective hydrogenation of phenylacetylene, designated as Ni @ G. The procedure of example 2 was followed, with a reaction time of 2h and without changing the other conditions. After the reaction, the composition of the reaction product was analyzed by gas chromatography, and the conversion of phenylacetylene was 0, and no formation of styrene or other by-products was detected.
Comparative example 2
The catalyst was prepared according to the method of example 1, except that the magnetic nickel graphene composite material obtained by high temperature pyrolysis was used as the catalyst, and no acid wash and noble metal monoatomic palladium loading was performed, which was recorded as Ni @ G to NA. The procedure of example 2 was followed, except that the conditions were unchanged. After the reaction, the composition of the reaction product was analyzed by gas chromatography, and the conversion of phenylacetylene was 0, and no formation of styrene or other by-products was detected.
Comparative example 3
The catalyst was prepared according to the method of example 1, except that the magnetic nickel graphene composite material obtained by pyrolysis only at high temperature was directly used as a carrier to load the noble metal palladium without acid washing, and the loading of palladium was still 0.1 wt.%, which is recorded as 0.1Pd/Ni @ G-NA. The procedure of example 2 was followed, all other conditions being unchanged. After the reaction, the composition of the reaction product was analyzed by gas chromatography to obtain phenylacetylene conversion of 46.6%, styrene selectivity of 98.3%, and total selectivity of other by-products of 1.7%.
Comparative example 4
The catalyst was prepared according to the method of example 1, except that by adjusting the support to Carbon Nanotubes (CNT), the loading of palladium was still 0.1 wt.%, noted 0.1 Pd/CNT. The procedure of example 2 was followed, except that the conditions were unchanged. After the reaction, the composition of the reaction product is analyzed by gas chromatography, so that the conversion rate of phenylacetylene is 27.5 percent, and the selectivity of styrene is more than 99 percent.
Comparative example 5
The catalyst was prepared according to the method of example 1, except that by adjusting the support to be defect-rich nanodiamond (ND @ G), the palladium loading was still 0.1 wt.%, noted 0.1Pd/ND @ G. The procedure of example 2 was followed, except that the conditions were unchanged. After the reaction, the composition of the reaction product is analyzed by gas chromatography, the conversion rate of phenylacetylene is 3.7 percent, and the selectivity of styrene is more than 99 percent.
Comparative example 6
The catalyst used was 5% commercial palladium on carbon catalyst in an amount of 1 mg. The procedure of example 2 was followed, except that the conditions were unchanged. After the reaction, the composition of the reaction product is analyzed by gas chromatography, thus obtaining the phenylacetylene conversion rate of 5.5 percent and the styrene selectivity of more than 99 percent.
As can be seen from comparison of comparative example 4, comparative example 5, comparative example 6 and example 2, the present application can achieve higher conversion rate and higher selectivity under mild conditions than the conventional carbon support and commercial palladium on carbon catalysts by using the Pd/Ni @ G catalyst.
By utilizing the hydrogenation catalyst, the excellent catalytic activity can be realized under the conditions of lower noble metal loading and mild conditions, the catalyst has good stability, and the catalyst is magnetic, can be separated, recovered and reused by an external magnetic field, is beneficial to reducing the cost and has better application prospect.
The above examples are given for reference only, and any embodiments similar to the present invention or extending from the scope of the present patent application are within the scope of the present invention.

Claims (6)

1. A magnetically-separable carbon-supported monatomic palladium catalyst, characterized in that: the catalyst takes palladium as an active material, a nickel-coated graphene composite material as a carrier, and the palladium is uniformly distributed on the surface of the nickel-coated graphene composite material carrier in a single-atom form;
the nickel-coated graphene composite material carrier is of a core-shell structure, nickel particles are a core, and graphene is a shell layer; the palladium is uniformly dispersed on the surface of a graphene shell in a monoatomic form and forms a bond with carbon atoms on the graphene defects;
the preparation method of the nickel-coated graphene composite material carrier comprises the steps of preparing a precursor by using nickel hydroxide and citric acid monohydrate, and carrying out high-temperature pyrolysis, wherein the mass ratio of the nickel hydroxide to the citric acid monohydrate is 1 (1-10); the preparation process comprises the following steps: putting nickel hydroxide and citric acid monohydrate into an oil bath in water according to a certain proportion, and stirring until the mixture is uniform to obtain a nickel citrate aqueous solution; after drying, putting the nickel citrate complex into a quartz boat for high-temperature pyrolysis carbonization treatment, wherein the high-temperature pyrolysis carbonization treatment process comprises the following steps: placing a nickel citrate raw material in an inert atmosphere of 500-900 ℃ and 30-80 ml/min for treatment, wherein the heating rate is 0.5-20 ℃/min, and the treatment time is 1-6 h, so as to obtain a magnetic nickel-coated graphene composite material; then carrying out acid washing treatment on the obtained carbon material, wherein the treatment process comprises the following steps: and (3) using excessive hydrochloric acid for pickling for 12-24 h, carrying out acid pickling at the temperature of 20-80 ℃, carrying out suction filtration after pickling, cleaning with deionized water and absolute ethyl alcohol, and drying in a vacuum drying oven at the temperature of 60 ℃ for 12-24 h to obtain the magnetic nickel-coated graphene composite material carbon carrier.
2. The magnetically separable carbon-supported monatomic palladium catalyst of claim 1, wherein: the catalyst has certain magnetism given to the carrier because the nickel particles are contained in the carrier.
3. The magnetically separable carbon-supported monatin palladium catalyst of claim 1, wherein: the content of palladium in the catalyst is 0.01-0.2 wt%.
4. The method of claim 1 for preparing a magnetically separable carbon-supported monatomic palladium catalyst, wherein: the method comprises the following steps:
(1) preparing a magnetic nickel-coated graphene composite material by using nickel hydroxide and citric acid monohydrate as raw materials;
(2) loading palladium species on the surface of the nickel-coated graphene composite material by a deposition precipitation method to obtain a magnetic palladium-based nickel-coated graphene composite material catalyst precursor; the deposition and precipitation process comprises the following steps: adding 30ml of deionized water into a 100ml round-bottom flask, putting 200mg of the magnetic palladium-based nickel-coated graphene composite material carrier obtained in the step (1) into the round-bottom flask, adjusting the pH to be alkaline under the condition of 100 ℃ oil bath, calculating the dosage of palladium nitrate according to the load of palladium in the catalyst, adjusting the dosage of a required amount of palladium nitrate solution to be neutral, dropwise adding the solution into the carrier solution in the flask, and stirring for 1 hour; standing and cooling to room temperature, carrying out vacuum drying for 12-24 h at 60 ℃ after suction filtration to obtain a magnetically separable carbon-supported monatomic palladium catalyst precursor;
(3) placing a magnetic palladium-based nickel-coated graphene composite catalyst precursor in a quartz tube, and carrying out reduction treatment in a hydrogen atmosphere, wherein the reduction treatment process comprises the following steps: reducing in a hydrogen atmosphere at the temperature of 100-200 ℃ for 1-3 h; and cooling to room temperature in an argon atmosphere of 10-30 ml/min after reduction treatment to obtain the magnetically separable carbon-supported monatomic palladium catalyst.
5. Use of a magnetically separable carbon-supported monatomic palladium catalyst according to claim 1, wherein: the catalyst is applied to the preparation of styrene by the selective hydrogenation of phenylacetylene.
6. Use of a magnetically separable carbon-supported monatomic palladium catalyst according to claim 5, wherein: in the selective hydrogenation reaction process of phenylacetylene, a reactant is phenylacetylene, a solvent is absolute ethyl alcohol, and a hydrogen source is hydrogen, wherein the ratio of the catalyst to the phenylacetylene is (25-40) mg: 1.85mmol, wherein the ratio of phenylacetylene to solvent is (1-5) mmol: (5-50) ml, wherein the use temperature of the catalyst is 20-80 ℃; the hydrogen pressure is 1-10 bar; the reaction time is 0.1-5 h.
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