阅读说明：本技术 碳纳米管内嵌金属粒子催化剂在合成气制低碳醇中的应用 (Application of carbon nano tube embedded metal particle catalyst in preparation of low-carbon alcohol from synthesis gas ) 是由 卢春山 周烨彬 应俊韬 李小年 张群峰 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嵌金属粒子催化剂在合成气制低碳醇反应中的应用,所述的催化剂由碳纳米管、氮掺杂的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氮掺杂的碳量子点,碳纳米管内壁镶嵌有金属纳米粒子；所述金属由活性金属和助剂金属组成,其中活性金属为铑,助剂金属为钯、铂、钌、铱、镍中的一种,活性金属与助剂金属质量比为10-50：1；所述氮掺杂的碳量子点尺寸在不大于10nm,氮含量在0.1-8.0wt％。本发明催化剂在碳量子点、内嵌金属粒子以及碳纳米管的限域效应协同作用下,实现了合成气制低碳醇反应中,高空速下也保持了高转化率、高乙醇选择性和高稳定性,催化效率高,催化剂寿命长。(The invention discloses an application of a catalyst with metal particles embedded in carbon nano tubes in the reaction of preparing low carbon alcohol from synthesis gas, wherein the catalyst consists of carbon nano tubes, nitrogen-doped carbon quantum dots and metal nano particles, the carbon nano tubes are single-walled or multi-walled carbon tubes with openings, the nitrogen-doped carbon quantum dots are loaded on the outer walls of the carbon nano tubes, and the metal nano particles are embedded in the inner walls of the carbon nano tubes; the metal consists of an active metal and an auxiliary metal, wherein the active metal is rhodium, the auxiliary metal is one of palladium, platinum, ruthenium, iridium and nickel, and the mass ratio of the active metal to the auxiliary metal is 10-50: 1; the size of the nitrogen-doped carbon quantum dot is not more than 10nm, and the nitrogen content is 0.1-8.0 wt%. The catalyst provided by the invention realizes the reaction of preparing low-carbon alcohol from synthesis gas under the synergistic effect of the carbon quantum dots, the embedded metal particles and the confinement effect of the carbon nano tubes, and also keeps high conversion rate, high ethanol selectivity and high stability at high airspeed, and has high catalytic efficiency and long catalyst life.)

1. The application of the catalyst with the metal particles embedded in the carbon nano tubes in the reaction of preparing the low carbon alcohol from the synthesis gas is characterized in that: the catalyst consists of a carbon nano tube, nitrogen-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 nitrogen-doped 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 consists of an active metal and an auxiliary metal, wherein the active metal is rhodium, and the auxiliary metal is one of palladium, platinum, ruthenium, iridium and nickel; the size of the nitrogen-doped carbon quantum dot is not more than 10nm, and the nitrogen content is 0.1-8.0 wt%; in the catalyst with metal particles embedded in the carbon nano tube, the loading capacity of nitrogen-doped carbon quantum dots is 0.5-8.0 wt%, the total loading capacity of metal is 0.1-10.0 wt%, and the mass ratio of active metal to auxiliary metal is 10-50: 1.

2. the use of claim 1, wherein: the size of the nitrogen-doped carbon quantum dots is 3.5-5.5 nm.

3. The use of claim 1, wherein: the carbon nano tube embedded metal particle catalyst 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 nitrogen-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 carbon nano tube embedded metal particle catalyst.

4. Use according to claim 3, characterized in that: the nitrogen-doped carbon quantum dot is prepared by the following method: adding deionized water, citric acid and ethylenediamine into a crucible at a ratio of 1-15 mL: 0.5-5.0 g: 0.01-1.0mL, mechanically stirring until the mixture is uniformly mixed; then placing the solution in a microwave oven with the power of 300-1500W and the heating time of 0.5-10min to obtain a light yellow carbon quantum dot solution; 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 of 100-10000 Dalton for dialysis treatment, wherein the carbon dot solution in the middle of 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 two-layer dialysis bag had a molecular weight cut-off of 4500-7000 daltons.

6. Use according to one of claims 3 to 5, characterized in that: step 2) is carried out as follows: and feeding the nitrogen-doped carbon quantum dot solution and the carbon nano tube subjected to acid treatment according to the loading capacity of the nitrogen-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:

placing the carbon nano tube embedded metal particle catalyst in a fixed bed reactor, wherein the reaction pressure is 2.0-3.0MPa, and the airspeed is 10000- ^-1，H ₂1-3 percent of/CO, and the reaction temperature is 200-250 ℃.

(I) technical field

The invention relates to an application of a catalyst with metal particles embedded in carbon nano tubes in preparation of low-carbon alcohol from synthesis gas.

(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 reaction ₃The 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 metal particles embedded in the carbon nano tube has the problems of complex process, difficult regulation and control of the deposition process in the metal particles, low proportion in the metal particle tube, low metal utilization rate and the like. In the reaction of preparing low-carbon alcohol from synthesis gas, the catalytic performance of the catalyst is still low in activity, high in reaction temperature, low in selectivity and the like.

Disclosure of the invention

The invention aims to provide application of a carbon nano tube embedded metal particle catalyst with nitrogen-doped carbon quantum dots loaded outside a tube in the reaction of preparing low-carbon alcohol from synthesis gas, and the catalyst realizes high reaction rate, high ethanol selectivity and high stability under high space velocity in the reaction of preparing low-carbon alcohol from synthesis gas under the synergistic effect of the carbon quantum dots, the embedded metal particles and the carbon nano tube in the confinement effect, and has high catalytic efficiency and long service life.

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

the invention provides an application of a catalyst with metal particles embedded in carbon nano tubes in the reaction of preparing low carbon alcohol from synthesis gas, wherein the catalyst consists of carbon nano tubes, nitrogen-doped carbon quantum dots and metal nano particles, the carbon nano tubes are single-walled or multi-walled carbon tubes with openings, the nitrogen-doped carbon quantum dots are loaded on the outer walls of the carbon nano tubes, and the metal nano particles are embedded in the inner walls of the carbon nano tubes; the metal consists of an active metal and an auxiliary metal, wherein the active metal is rhodium, and the auxiliary metal is one of palladium, platinum, ruthenium, iridium and nickel; the size of the nitrogen-doped carbon quantum dot is not more than 10nm, and the nitrogen content is 0.1-8.0 wt%; in the catalyst with metal particles embedded in the carbon nano tube, the loading capacity of nitrogen-doped carbon quantum dots (the mass ratio of the carbon quantum dots to the carbon nano tube) is 0.5-8.0 wt%, the total loading capacity of metal is 0.1-10.0 wt%, and the mass ratio of active metal to auxiliary metal is 10-50: 1.

Preferably, in the catalyst for depositing metal particles in the carbon nanotube, the loading amount of nitrogen-doped 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 nitrogen-doped carbon quantum dots is 3.5-5.5 nm.

Preferably, the carbon nanotube embedded metal particle catalyst 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 room temperature after the reflux treatment is finished, washing with water until the 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 nitrogen-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 carbon nano tube embedded metal particle catalyst.

According to the preparation method, the nitrogen-doped carbon quantum dots and the carbon nano tubes are rigidly absorbed 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 nitrogen-doped carbon quantum dots, wherein the electrical enrichment of nitrogen atoms is more 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 150m ²/g。

In the present invention, the nitrogen-doped carbon quantum dots can be prepared by referring to the prior art. Preferably, the nitrogen-doped carbon quantum dots are prepared by using citric acid and ethylenediamine as raw materials and utilizing esterification reaction or amidation reaction of carboxyl and amino under the assistance of microwaves to generate the nitrogen-doped carbon dots, and the electrical enrichment of heteroatoms is favorable for metal ions to enter the tube and be loaded on the inner wall of the tube. The microwave method is simple to operate and has high nitrogen doping content. The specific process is as follows: adding deionized water, citric acid and ethylenediamine into a crucible at a ratio of 1-15 mL: 0.5-5.0 g: 0.01-1.0mL, and mechanically stirring until the mixture is uniformly mixed; then placing the solution in a microwave oven with the power of 300-1500W and the heating time of 0.5-10min to obtain a light yellow carbon quantum dot solution; 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 of 100-10000 Dalton for dialysis treatment, the carbon dot solution in the middle of the two layers can be the carbon dot solution, and finally, the carbon dot solution is concentrated to the concentration of 0.5-25.0mg/L under the condition of shading low temperature. As a further preference, the two-layer dialysis bag has a molecular weight cut-off of 4500-.

Step 2) of the present invention is preferably carried out as follows: and feeding the nitrogen-doped carbon quantum dot solution and the carbon nano tube subjected to acid treatment according to the loading capacity of the nitrogen-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:

the catalyst is placed in a fixed bed reactor (the inner diameter is 6mm), the reaction pressure is 2.0-3.0MPa, and the space velocity is 10000- ^-1，H ₂1-3 percent of/CO, and the reaction temperature is 200-250 ℃. Before the reaction, the catalyst is not specially treated. After the gas tail gas is condensed by a cold trap, the gas phase enters a gas chromatography with a TCD detector to analyze the gas phase composition, and the liquid phase enters a gas chromatography with an FID detector to analyze the selectivity.

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

1) in the catalyst with embedded metal particles in the carbon nano tube, the catalyst structure is designed to be externally loaded with nitrogen-doped carbon quantum dots in a regulating and controlling manner, metal particles are embedded in the carbon nano tube, the electron-donating property of the nitrogen-doped carbon quantum dots, the carbon tube to the metal particles and the confinement effect of the carbon tube to reactant molecules are realized, and the catalyst generates specific catalytic property. Under the synergistic effect of the carbon quantum dots, the embedded metal particles and the confinement effect of the carbon nano tubes, the invention realizes the reaction of preparing low-carbon alcohol from synthesis gas, maintains high reaction rate, high ethanol selectivity and high stability at high airspeed, and has high catalytic efficiency and long catalyst life.

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 metal utilization rate 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: