阅读说明：本技术 碳纳米管内沉积金属粒子催化剂在苯选择性催化加氢合成环己烷的反应中的应用 (Application of catalyst for depositing metal particles in carbon nano tube in reaction of synthesizing cyclohexane through selective catalytic hydrogenation of benzene ) 是由 卢春山 张雪洁 聂娟娟 李小年 马磊 于 2019-08-27 设计创作，主要内容包括：本发明公开了一种碳纳米管内沉积金属粒子催化剂在苯选择性催化加氢合成环己烷的反应中的应用,所述的催化剂由碳纳米管、磷掺杂碳量子点和金属纳米粒子组成,所述的碳纳米管为开孔的单壁或多壁碳管,碳纳米管外壁负载有碳量子点,碳纳米管内壁镶嵌有金属纳米粒子；所述金属为钯、铂、金、钌、铱、镍、钴中的一种；所述的磷掺杂的碳量子点尺寸不大于10nm,磷含量在0.1-8.0wt％；所述碳纳米管内沉积金属粒子催化剂中,磷掺杂的碳量子点负载量为0.5-8.0wt％,金属的负载量为0.1-10.0wt％。该催化剂应用于苯选择性催化加氢合成环己烷的反应时,在碳量子点、内嵌金属粒子以及碳纳米管的限域效应协同作用下,实现了高转化率、高选择性和高稳定性,催化效率高,催化剂寿命长。(The invention discloses an application of a catalyst for depositing metal particles in a carbon nano tube in the reaction of synthesizing cyclohexane by selective catalytic hydrogenation of benzene, wherein the catalyst consists of the carbon nano tube, phosphorus-doped carbon quantum dots and metal nano particles, the carbon nano tube is a single-walled or multi-walled carbon tube with openings, the carbon quantum dots are loaded on the outer wall of the carbon nano tube, and the metal nano particles are embedded in the inner wall of the carbon nano tube; the metal is one of palladium, platinum, gold, ruthenium, iridium, nickel and cobalt; the size of the phosphorus-doped carbon quantum dot is not more than 10nm, and the phosphorus content is 0.1-8.0 wt%; in the catalyst for depositing metal particles in the carbon nano tube, the load of the carbon quantum dots doped with phosphorus is 0.5-8.0 wt%, and the load of metal is 0.1-10.0 wt%. When the catalyst is applied to the reaction of synthesizing cyclohexane by benzene selective catalytic hydrogenation, high conversion rate, high selectivity and high stability are realized under the synergistic effect of the carbon quantum dots, the embedded metal particles and the confinement effect of the carbon nano tube, the catalytic efficiency is high, and the service life of the catalyst is long.)

1. The application of the catalyst for depositing metal particles in the carbon nano tube in the reaction of synthesizing cyclohexane by selective catalytic hydrogenation of benzene is characterized in that: the catalyst consists of a carbon nano tube, phosphorus-doped carbon quantum dots and metal nano particles, wherein the carbon nano tube is a single-walled or multi-walled carbon tube with an opening, the carbon quantum dots are loaded on the outer wall of the carbon nano tube, and the metal nano particles are embedded in the inner wall of the carbon nano tube; the metal is one of palladium, platinum, gold, ruthenium, iridium, nickel and cobalt; the size of the phosphorus-doped carbon quantum dot is not more than 10nm, and the phosphorus content is 0.1-8.0 wt%; in the catalyst for depositing metal particles in the carbon nano tube, the load of the carbon quantum dots doped with phosphorus is 0.5-8.0 wt%, and the load of metal is 0.1-10.0 wt%.

2. The use of claim 1, wherein: the size of the phosphorus-doped carbon quantum dots is 2.5-5.5 nm.

3. The use of claim 1, wherein: the catalyst for depositing metal particles in the carbon nano tube is prepared by the following method:

1) placing the carbon nano tube in concentrated nitric acid, heating and refluxing, cooling to room temperature after the heating and refluxing treatment, washing with water until filtrate is neutral, and drying to obtain the carbon nano tube subjected to acid treatment;

2) preparing a phosphorus-doped carbon quantum dot solution and the carbon nano tube subjected to acid treatment obtained in the step 1) into a dispersion liquid, fully stirring to enable the carbon quantum dots to be loaded on the outer wall of the carbon nano tube, and performing suction filtration and drying to obtain the carbon nano tube loaded with the carbon dots;

3) preparing the carbon nano tube loaded with the carbon dots obtained in the step 2) and deionized water into slurry, adding aqueous solution containing metal ions under the stirring state, forming complex anions by the metal ions and chloride ions in the aqueous solution, fully stirring, performing suction filtration, washing until the pH value of filtrate is neutral, and drying to obtain the catalyst of metal particles deposited in the carbon nano tube.

4. Use according to claim 3, characterized in that: the phosphorus-doped carbon quantum dot is prepared by the following method: putting humic acid and ethanol into a beaker, wherein the proportion is 0.5-5.0 g: 5-100mL, mechanically stirring until the mixture is uniformly mixed; then transferring the mixture into a hydrothermal kettle, carrying out hydrothermal treatment at the temperature of 120-; then carrying out centrifugal treatment under the condition that the rotating speed is 20000r/min, transferring the supernatant into a two-layer dialysis bag with the molecular weight cutoff of 100-10000 Dalton for dialysis treatment, wherein the carbon dot solution between the two layers is the carbon dot solution, and finally concentrating under the condition of shading low temperature until the concentration is 0.5-25.0 mg/L.

5. The use of claim 4, wherein: the cut-off of the dialysis bag was 3000-7000 dalton.

6. Use according to one of claims 3 to 5, characterized in that: step 2) is carried out as follows: and feeding the phosphorus-doped carbon quantum dot solution and the carbon nano tube subjected to acid treatment according to the load capacity of the phosphorus-doped carbon quantum dots, stirring for 10-60min, and drying the filtered solid particles in a vacuum oven at the temperature of 50-100 ℃ for 2-15h to obtain the carbon nano tube loaded with the carbon dots.

7. Use according to one of claims 3 to 5, characterized in that: step 3) is carried out as follows: the carbon nano tube loaded with the carbon dots obtained in the step 2) is mixed with water according to the feeding ratio of the carbon nano tube loaded with the carbon dots to the water of 1 g: preparing 5-35ml of prepared slurry, adding corresponding aqueous solution containing metal ions according to the metal loading capacity at the temperature of 5-40 ℃ under the stirring state, wherein the dropping speed of the aqueous solution containing the metal ions is 1d/1-10s, continuing stirring for 2-6h after the dropping is finished, performing suction filtration, washing until the pH value is neutral, and drying for 3-15h at the temperature of 50-100 ℃ to obtain the catalyst.

8. Use according to claim 1 or 2, characterized in that: the application method comprises the following steps: uniformly mixing a catalyst with metal particles deposited in a carbon nanotube and quartz sand particles with the granularity of 0.5-2mm, putting the mixture into a fixed bed reactor, introducing hydrogen for pretreatment for 0.5-2h at 50-150 ℃, then heating to 250 ℃ and keeping the temperature constant; setting the temperature of the container containing benzene at 20-50 deg.c, and flowing 1-10ml/min hydrogen gas through the container to bring benzene vapor into the reactor for benzene hydrogenating reaction to produce cyclohexane.

(I) technical field

The invention relates to an application of a catalyst for depositing metal particles in a carbon nano tube in the reaction of synthesizing cyclohexane by selective catalytic hydrogenation of benzene.

(II) technical background

Carbon nanotubes have structural defects, curved surfaces, unique lumen structures, and electrical conductivity properties, and are excellent catalytic materials. Based on the collision theory of chemical reaction, the reaction space in the tube is obviously reduced, and the unique interaction of reactants and products with the inner wall of the carbon nano tube can influence the progress of the chemical reaction. Santis et al have learned through theoretical calculations that when the chemical reaction is confined to a small pore size, the reaction kinetics change significantly and the reaction rate can jump by orders of magnitude. Lu et al calculated the mechanism of the limited-domain reaction in carbon nanotubes using DFT theory, found that after the reaction limited-domain was inside the carbon nanotubes, the barrier affecting the reaction progress was significantly reduced, and the reactivity of the reactants in the tubes was enhanced with the reduction of the tube diameter of the carbon nanotubes. Therefore, the catalyst with the carbon nano tubes embedded with the metal particles can be used for preparing ethanol by converting synthesis gas, performing Fischer-Tropsch reaction, performing benzene hydrogenation reaction and performing NH reaction₃The catalyst shows excellent catalytic performance in the decomposition reaction.

The preparation method of the prior metal catalyst loaded in the tube mainly comprises the following steps: in-situ filling methods, gas phase filling methods, and liquid phase filling methods. The in-situ filling method adopts the means of an electric arc method, a microwave method and the like to generate metal or compound in situ in the cavity channel and the shell layer of the carbon nano tube in the process of preparing the carbon nano tube. Generally, the in-situ filling method can fill a plurality of metals with higher melting points and higher surface tension, but the in-situ filling method has lower filling yield, and some metal carbides or metal particles are assembled into the carbon nanotube shell during the filling process. The gas phase filling method is a method of performing a high-temperature reaction in a gas phase. That is, the carbon nanotubes are mixed with the filler under a certain pressure and temperature, and the filler is vaporized by heating and introduced into the carbon nanotubes. The gas phase method has the advantages that only gas capable of reacting with the carbon nano tube is needed in the reaction, more reagents are not needed, the environment is not polluted, and other substances are not introduced into the system; the method has the disadvantages that the carbon nano tube has low opening rate, needs high temperature of 500-1000 ℃, is difficult to control proper reaction time and temperature, and is not easy to fill because amorphous carbon is accumulated in a tube cavity. The liquid phase filling method mixes and grinds the filler and the carbon nano tube to ensure that the filler and the carbon nano tube are fully contacted, then the temperature is raised to be higher than the melting point of the filler, and the melted filler enters the interior of the carbon nano tube under the capillary action. The filling of salts such as metal halides and oxides is usually carried out by melting the filling.

However, the existing preparation method of the carbon nanotube embedded metal particles has the defects of complex process, difficult regulation, low catalyst product yield and the like. In the benzene hydrogenation reaction, the catalytic performance of the catalyst still has the problems of low activity, low selectivity and the like.

Disclosure of the invention

The invention aims to provide application of a catalyst for depositing metal particles in a carbon nano tube with carbon quantum dots loaded on the outer wall of the tube in the reaction of synthesizing cyclohexane by selective catalytic hydrogenation of benzene, and the catalyst realizes high conversion rate, high selectivity and high stability, high catalytic efficiency and long service life of the catalyst under the synergistic effect of the carbon quantum dots, the embedded metal particles and the confinement effect of the carbon nano tube.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides an application of a catalyst for depositing metal particles in a carbon nano tube in the reaction of synthesizing cyclohexane by selective catalytic hydrogenation of benzene, wherein the catalyst consists of the carbon nano tube, phosphorus-doped carbon quantum dots and metal nano particles, the carbon nano tube is a single-wall or multi-wall carbon tube with openings, the carbon quantum dots are loaded on the outer wall of the carbon nano tube, and the metal nano particles are embedded in the inner wall of the carbon nano tube; the metal is one of palladium, platinum, gold, ruthenium, iridium, nickel and cobalt; the size of the phosphorus-doped carbon quantum dot is not more than 10nm, and the phosphorus content is 0.1-8.0 wt%; in the catalyst for depositing metal particles in the carbon nano tube, the load of the carbon quantum dots doped with phosphorus (the mass ratio of the carbon quantum dots to the carbon nano tube) is 0.5-8.0 wt%, and the load of metal is 0.1-10.0 wt%.

Preferably, in the catalyst for depositing metal particles in the carbon nanotube, the loading amount of the carbon quantum dots is 0.5-5.0 wt%. Preferably, the loading of metal in the catalyst is 0.5 to 5.0 wt%.

Preferably, the size of the phosphorus-doped carbon quantum dots is 2.5-5.5 nm.

Preferably, the catalyst for depositing metal particles in the carbon nano tube can be prepared by the following method:

1) placing the carbon nano tube in concentrated nitric acid (65-68 wt%) for heating reflux treatment, cooling to an air temperature after the reflux treatment is finished, washing with water until filtrate is neutral, and drying to obtain the carbon nano tube subjected to acid treatment; because the freshly prepared carbon nano tube is a tube which grows out on metal particles and is usually closed, in order to utilize the space in the tube and remove the metal particles of the long carbon tube, concentrated nitric acid is adopted for pretreatment;

2) preparing a phosphorus-doped carbon quantum dot solution and the carbon nano tube subjected to acid treatment obtained in the step 1) into a dispersion liquid, fully stirring to enable the carbon quantum dots to be loaded on the outer wall of the carbon nano tube, and performing suction filtration and drying to obtain the carbon nano tube loaded with the carbon dots;

3) preparing the carbon nano tube loaded with the carbon dots obtained in the step 2) and deionized water into slurry, adding aqueous solution containing metal ions under the stirring state, forming complex anions by the metal ions and chloride ions in the aqueous solution, fully stirring, performing suction filtration, washing until the pH value of filtrate is neutral, and drying to obtain the catalyst of metal particles deposited in the carbon nano tube.

According to the preparation method, the phosphorus-doped carbon quantum dots and the carbon nano tubes are adsorbed on the outer walls of the carbon nano tubes through pi-pi conjugation so as to be converted into excellent electron-donating centers, and then metal complex ions with negative charges are induced to spontaneously enter the tubes and deposit on the inner walls by utilizing the electron-donating characteristics of the phosphorus-doped carbon quantum dots, wherein the electrical enrichment property of phosphorus atoms is favorable for the metal ions to enter the tubes and be loaded on the inner walls of the tubes, so that the small-particle-size and uniform distribution of metal active components in the carbon nano tubes is realized.

In the step 1), the nitric acid treatment is a conventional treatment method for opening the carbon tube and removing residual metal. Preferably, in the acid treatment process of the carbon nano tube in the step 1), the ratio of the carbon nano tube to the nitric acid is 1-10 g: 20-100ml, the treatment temperature is 45-95 ℃, and the condensation reflux is carried out for 2-15 h. Preferably, the drying conditions are: drying at 50-100 deg.C for 1-10 hr. Preferably, the diameter distribution of the carbon nanotubes is 20-40nm, and the specific surface area is more than 150m²/g。

In the invention, the phosphorus-doped carbon quantum dots can be prepared by referring to the prior art. Preferably, the phosphorus-doped carbon quantum dots are prepared by taking humic acid as a raw material and performing hydrothermal synthesis, and the specific process is as follows: putting humic acid and ethanol into a beaker in a ratio of 0.5-5.0g to 5-100mL, and mechanically stirring until the humic acid and the ethanol are uniformly mixed; then transferring the mixture into a hydrothermal kettle, carrying out hydrothermal treatment at the temperature of 120-; then, centrifugal treatment is carried out (organic matter particles which are not completely carbonized are removed) under the condition that the rotating speed is 20000r/min, supernatant is transferred into a two-layer dialysis bag with the molecular weight cutoff of 100-10000 Dalton for dialysis treatment, the carbon dot solution in the middle of the two layers is the carbon dot solution, and finally, the solution is concentrated to the concentration of 0.5-25.0mg/L under the condition of shading low temperature. In the method, the size of the quantum dots can be controlled by controlling the molecular weight cut-off of the dialysis bag. As a further preference, the dialysis bag has a molecular weight cut-off of 3000-7000 Dalton, more preferably 3500-6500 Dalton.

Step 2) of the process is preferably carried out as follows: and feeding the phosphorus-doped carbon quantum dot solution and the carbon nano tube subjected to acid treatment according to the load capacity of the phosphorus-doped carbon quantum dots, stirring for 10-60min, and drying the filtered solid particles in a vacuum oven at the temperature of 50-100 ℃ for 2-15h to obtain the carbon nano tube loaded with the carbon dots.

Step 3) of the present invention is preferably carried out as follows: preparing the carbon nano tube loaded with the carbon dots obtained in the step 2) into slurry according to the feeding ratio of the carbon nano tube loaded with the carbon dots to water of 1 g: 5-35ml, adding the corresponding aqueous solution containing the metal ions according to the metal loading capacity at the temperature of 5-40 ℃ under the stirring state, wherein the dropping speed of the aqueous solution containing the metal ions is 1d/1-10s, continuously stirring for 2-6h after dropping, performing suction filtration, washing until the pH value is neutral, and drying for 3-15h at the temperature of 50-100 ℃ to obtain the catalyst.

Preferably, the application method comprises the following steps: uniformly mixing a catalyst with metal particles deposited in a carbon nanotube and quartz sand particles with the granularity of 0.5-2mm, putting the mixture into a fixed bed reactor, introducing hydrogen for pretreatment for 0.5-2h at 50-150 ℃, then heating to 250 ℃ and keeping the temperature constant; setting the temperature of the container containing benzene at 20-50 deg.c, and flowing 1-10ml/min hydrogen gas through the container to bring benzene vapor into the reactor for benzene hydrogenating reaction to produce cyclohexane. The hydrogenation product was analyzed on-line by Agilent7890A gas chromatography.

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

1) in the process of depositing metal particle catalyst in carbon nanotube, the present invention designs the catalyst structure into carbon quantum dot supported outside the tube, embedding metal particle inside the tube, the electron donating characteristic of the carbon quantum dot, the domain limiting effect of the carbon tube on the metal particle and the reactant molecule, and makes the catalyst produce specific catalytic characteristic. When the catalyst is applied to the reaction of synthesizing cyclohexane by benzene selective catalytic hydrogenation, high conversion rate, high selectivity and high stability are realized under the synergistic effect of the carbon quantum dots, the embedded metal particles and the confinement effect of the carbon nano tube, the catalytic efficiency is high, and the service life of the catalyst is long.

2) In the preparation method of the catalyst, metal ions of anions are driven to the inner wall of the carbon tube through electrostatic action by virtue of the electron-rich characteristic of the carbon quantum dots loaded on the outer wall of the carbon tube, so that the utilization rate of metals is remarkably improved. The method is simple, convenient and easy to control, and has low cost.

(IV) description of the drawings

A and b in fig. 1 are electron micrographs of the catalysts prepared in comparative example 1 and example 1, respectively.

Fig. 2 is a graph showing the percentage of metal particles in carbon nanotubes in the catalysts prepared in example 1, comparative example 1, and comparative example 3, where 1 is comparative example 1; 2 is comparative example 3; example 3 data from randomly selected 500 particles (TEM characterization) are obtained for example 1.

(V) detailed description of the preferred embodiments

The technical solution of the present invention is specifically described below with specific examples, but the scope of the present invention is not limited thereto: