CN111282586A

CN111282586A - Preparation method and application of in-situ alumina coated titanium carbide catalyst

Info

Publication number: CN111282586A
Application number: CN202010210280.4A
Authority: CN
Inventors: 梁诗景; 詹辉; 江莉龙
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2020-03-24
Filing date: 2020-03-24
Publication date: 2020-06-16
Anticipated expiration: 2040-03-24
Also published as: CN111282586B

Abstract

The invention discloses a preparation method and application of a super-hydrophobic in-situ alumina coated titanium carbide catalyst, and belongs to the technical fields of material preparation, electrocatalysis and fine chemical engineering. The electrocatalyst is prepared by taking sodium fluoride, commercial titanium aluminum carbide, N-methyl pyrrolidone, sodium carbonate, sodium hydroxide and polytetrafluoroethylene as raw materials, feeding in batches, heating and stirring under mild conditions, and using etched and dissolved aluminum ions as an aluminum source. The electrocatalyst prepared by the invention has good stability, large specific surface area, good electrocatalysis performance, good oxidation resistance, high thermal stability and the like. The preparation method has the advantages of simple and convenient preparation process, low energy consumption, low cost and great application potential.

Description

Preparation method and application of in-situ alumina coated titanium carbide catalyst

Technical Field

The invention belongs to the technical fields of material preparation, electrocatalysis and fine chemical engineering, and particularly relates to a preparation method and application of a super-hydrophobic in-situ alumina coated titanium carbide catalyst.

Background art ammonia is the second largest chemical produced in the world. Global ammonia production in 2015 approaches 1.46 million tons, with a projected 40% increase by 2050, and amino fertilizers help to supply food for the globally growing population (about 100 million by 2050). Ammonia can also play an important role in the development of clean transportation and can be used directly in ammonia fuel cells or indirectly in hydrogen fuel cells. Ammonia can be a superior energy carrier for hydrogen (e.g., 17.6 wt% hydrogen in liquid ammonia versus 12.5 wt% methanol) as compared to other conventional fuels. Therefore, sustainable ammonia production is critical to food energy chemistry.

Currently, ammonia production relies primarily on the industrial Haber-Bosch process. The Haber-Bosch process entails ammonia synthesis at high temperature and pressure using pure hydrogen, which is typically derived from steam reforming of natural gas; meanwhile, a large amount of carbon dioxide gas is generated in the steam reforming process of natural gas, and therefore, ammonia production is an important factor causing climate change. Finding new alternative methods for ammonia synthesis is of great scientific interest at present. Although the literature is still rare, a number of N-passes have been reported₂And direct production of NH by electroreduction of water or steam₃Electrocatalytic study of (1). Most of the research on the electrochemical production of ammonia is based on solid-state electrolytes at high temperatures and pressures. Other studies are also based on liquid electrolytes, such as organic solvents, ionic liquids, molten salts, high-pressure or ambient-pressure aqueous electrolytes. In these studies, transition metal complexes and materials have been generally used as catalysts. If solvent water is used as the hydrogen proton source directly instead of hydrogen as the hydrogen protonThe method has the advantages of greatly saving the cost in the ammonia synthesis process, avoiding the emission of carbon dioxide in the reforming process, and reducing the influence on the environment, so the aqueous electrolyte method has the characteristics of simplicity and low cost. However, aqueous electrolyte approaches suffer from competitive hydrogen evolution, which limits overall efficiency, resulting in low overall reaction rates. Until now, the faradaic efficiency of aqueous reactions under ambient conditions has not substantially exceeded 10%.

Titanium carbide is a new two-dimensional material, with a single layer thickness typically less than 1 nm and lateral dimensions ranging from nanometers to micrometers. In addition, titanium carbide has abundant surface functional groups, such as hydroxyl, oxygen or fluorine. In the presence of complete metal atomic layers and surface functional groups, the titanium carbide has good electronic conductivity and hydrophilic property, and meanwhile, the titanium carbide has a highly ordered structure, and the property of the titanium carbide can be predicted by theoretical calculation. The titanium carbide has larger internal surface area due to the layered structure, the interplanar spacing of the titanium carbide after the intercalation of the N-methylpyrrolidone is further increased, the internal surface area is further enlarged, and the interlayer space of the titanium carbide is beneficial to the enrichment of nitrogen, so that the titanium carbide can become possible to be electrically reduced for nitrogen fixation.

Disclosure of Invention

The invention aims to provide a preparation method of a super-hydrophobic in-situ alumina coated titanium carbide catalyst and application of the catalyst in electrocatalysis.

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

a super-hydrophobic in-situ alumina coated titanium carbide catalyst is prepared by taking sodium fluoride, commercial titanium aluminum carbide, N-methyl pyrrolidone, sodium carbonate, sodium hydroxide and polytetrafluoroethylene as raw materials, feeding in batches, heating and stirring under mild conditions, and using aluminum ions dissolved out by etching as an aluminum source to prepare the high-performance super-hydrophobic in-situ alumina coated titanium carbide electrocatalyst for electrocatalytic nitrogen fixation, and specifically comprises the following steps:

1) take 0.4 g Ti₃AlC₂And 50 mL of NMP solution containing NaF (6 mol/L) were placed in a plastic reactor and heated at 60-100 deg.CStirring and heating are carried out, the rotating speed is 1000 r/min, and the reaction time is 1-4 h.

2) Adding 0.05-0.2 g of sodium carbonate and 50-100 muL of polytetrafluoroethylene PTFE emulsion (content 40 wt%) into the suspension obtained by the reaction, adjusting the pH value to 10 by using 4 mol/L of sodium hydroxide solution, continuously stirring and reacting for 0.5-2 h at 60 ℃ and 1000 r/min, and then placing the mixture into an ultrasonic machine (frequency 40 kHz and power 100W) for ultrasonic reaction for 1 h.

3) And centrifuging the reaction solution in a centrifugal machine of 3500 r/min to remove the solvent, and washing the reaction solution by using absolute ethyl alcohol and deionized water respectively until the ion solubility of the solution is lower than 10 ppm. And finally, transferring the sample into a freeze dryer to carry out freeze drying for 6 hours at the temperature of-18 ℃ to obtain a sample.

The obtained super-hydrophobic in-situ alumina coated titanium carbide catalyst is mainly used for electrochemically synthesizing ammonia. The method specifically comprises the following steps: dispersing 2 mg of the catalyst in a dispersion liquid consisting of 225 muL ethanol, 225 muL water and 50 muL nafion, and after one hour of ultrasonic dispersion, taking 50 muL dispersed liquid drops in 1 x 1cm^-2The working electrode is made on the carbon paper, and then the traditional three-electrode system is used for electrocatalytic synthesis of ammonia.

The invention has the following remarkable advantages:

(1) the preparation method has simple preparation conditions, and the N-methylpyrrolidone is firstly utilized to intercalate the titanium carbide material, so that the prepared material layer spacing is increased, more surface defects can be exposed, and more reaction active centers can be provided.

(2) The electrode material is subjected to hydrophobic treatment by creatively utilizing the polytetrafluoroethylene solution, so that the material has super-hydrophobicity, the hydrogen evolution reaction in electrochemical nitrogen fixation is inhibited, and the Faraday efficiency of the nitrogen fixation reaction is improved.

(3) The alumina coating is creatively generated in situ to form a strong composite structure of alumina-titanium carbide-polytetrafluoroethylene, and a novel super-hydrophobic in situ alumina coated titanium carbide catalyst is prepared for the first time.

(4) The super-hydrophobic in-situ alumina coated titanium carbide catalyst is creatively prepared by using N-methyl pyrrolidone, polytetrafluoroethylene, sodium carbonate and aluminum ions generated by etching in a synergistic manner, and the problems that the preparation process of the previously reported titanium carbide catalyst material is complex, and the alumina coating and the super-hydrophobicity of the catalyst can be realized by multiple processes are solved.

Drawings

FIG. 1 is an X-ray powder diffraction pattern (XRD) of the superhydrophobic in-situ alumina-coated titanium carbide catalyst obtained in example 1.

FIG. 2 is a scanning electron microscope image of the super-hydrophobic in-situ alumina-coated titanium carbide catalyst electrocatalyst obtained in example 2.

FIG. 3 is a graph comparing the ammonia content in the solution after electrochemical nitrogen fixation of a blank sample and bias voltage applied to the superhydrophobic in-situ alumina-coated titanium carbide catalyst obtained in example 2 without bias voltage.

FIG. 4 is a test of hydrophilicity and hydrophobicity of the titanium carbide material prepared in example 1.

Detailed Description

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1

Take 0.4 g Ti₃AlC₂And 50 mL of NMP solution containing NaF (6 mol/L) are put into a plastic reactor, stirred and heated at 60 ℃, the rotating speed is 1000 r/min, and the reaction time is 4 h. 0.2 g of sodium carbonate and 50 muL of PTFE emulsion (content: 40%) are added into the suspension obtained by the reaction, the pH value is adjusted to 10 by using 4 mol/L sodium hydroxide solution, the reaction is continuously stirred for 0.5 h at 60 ℃ and 1000 r/min, and then the mixture is placed in an ultrasonic machine (frequency: 40 kHz, power: 100W) for ultrasonic reaction for 1 h. And centrifuging the reaction solution in a centrifugal machine of 3500 r/min to remove the solvent, and washing the reaction solution by using absolute ethyl alcohol and deionized water respectively until the ion solubility of the solution is lower than 10 ppm. And finally, transferring the sample into a freeze dryer for freeze drying to obtain a sample.

Example 2

Take 0.4 g Ti₃AlC₂And 50 mL of deionized water containing NaF (6 mol/L) was put into a moldIn the material reactor, stirring and heating are carried out at 80 ℃, the rotating speed is 1000 r/min, and the reaction time is 2 h. Adding 0.05 g of sodium carbonate and 60 muL of PTFE emulsion (content: 40%) into the suspension obtained by the reaction, adjusting the pH value to 10 by using 4 mol/L of sodium hydroxide solution, continuously stirring and reacting for 0.5 h at 60 ℃ and 1000 r/min, and then placing the mixture into an ultrasonic machine (frequency: 40 kHz, power: 100W) for ultrasonic reaction for 1 h. And centrifuging the reaction solution in a centrifugal machine of 3500 r/min to remove the solvent, and washing the reaction solution by using absolute ethyl alcohol and deionized water respectively until the ion solubility of the solution is lower than 10 ppm. And finally, transferring the sample into a freeze dryer for freeze drying to obtain a sample.

Example 3

Take 0.4 g Ti₃AlC₂And 50 mL of deionized water containing NaF (6 mol/L) are put into a plastic reactor, stirred and heated at 80 ℃, the rotating speed is 1000 r/min, and the reaction time is 1 h. 0.2 g of sodium carbonate and 100 muL of PTFE emulsion (content: 40%) are added into the suspension obtained by the reaction, the pH value is adjusted to 10 by using 4 mol/L of sodium hydroxide solution, the reaction is continuously stirred for 2 hours at 60 ℃ and 1000 r/min, and then the mixture is placed in an ultrasonic machine (frequency: 40 kHz and power: 100W) for ultrasonic reaction for 1 hour. And centrifuging the reaction solution in a centrifugal machine of 3500 r/min to remove the solvent, and washing the reaction solution by using absolute ethyl alcohol and deionized water respectively until the ion solubility of the solution is lower than 10 ppm. And finally, transferring the sample into a freeze dryer for freeze drying to obtain a sample.

Example 4

Take 0.4 g Ti₃AlC₂And 50 mL of deionized water containing NaF (6 mol/L) are put into a plastic reactor, stirred and heated at 100 ℃, the rotating speed is 1000 r/min, and the reaction time is 1 h. Adding 0.1 g of sodium carbonate and 60 muL of PTFE emulsion (content: 40%) into the suspension obtained by the reaction, adjusting the pH value to 10 by using 4 mol/L of sodium hydroxide solution, continuously stirring and reacting for 0.5 h at 60 ℃ and 1000 r/min, and then placing the mixture into an ultrasonic machine (frequency: 40 kHz, power: 100W) for ultrasonic reaction for 1 h. And centrifuging the reaction solution in a centrifugal machine of 3500 r/min to remove the solvent, and washing the reaction solution by using absolute ethyl alcohol and deionized water respectively until the ion solubility of the solution is lower than 10 ppm. Finally, move into coldAnd (5) carrying out freeze drying by using a freeze dryer to obtain a sample.

Application example 1

Dispersing 2 mg of a sample prepared by the method in a dispersion liquid consisting of 225 muL ethanol, 225 muL water and 50 muL nafion, and after one hour of ultrasonic dispersion, dropping 50 muL of the dispersion liquid in 1 x 1cm^-2The working electrode is made on the carbon paper. Then the traditional three-electrode system is used for electrocatalytic synthesis of ammonia.

Fig. 1 is an X-ray powder diffraction pattern of the titanium carbide electrocatalysts obtained in examples 1 to 4, and it can be seen from fig. 1 that the two-dimensional layered titanium carbide is successfully prepared by the method of the present invention, and after N-methylpyrrolidone intercalation treatment, the crystal plane (002), i.e., the peak position at 2 θ, is shifted forward, indicating that the interplanar spacing is significantly increased. The coating modification of the aluminum oxide and the polytetrafluoroethylene does not change the crystallinity of the titanium carbide material.

FIG. 2 is a comparison of scanning electron micrographs of unreacted titanium aluminum carbide and example 2. As can be seen in the figure, the titanium aluminum carbide is a dense layered structure (FIG. 2, left). The two-dimensional layered titanium carbide material prepared by the method is of a nano-sheet stacked structure, and the aluminum-titanium carbide middle aluminum layer can be clearly seen to be stripped (figure 2, right). And the titanium carbide surface is covered with a slightly rough aluminum oxide and polytetrafluoroethylene composite layer.

Fig. 3 shows the ammonia yield after the nitrogen fixation reaction in the blank experiment under argon atmosphere using a three-electrode system with-0.3V bias and without bias after the titanium carbide material prepared in example 1 was prepared into an electrocatalytic working electrode, and the blank experiment was performed directly using 1cm by 1cm carbon paper without any solution added dropwise as a blank sample. The electrochemical reaction uses three-electrode system, the preparation electrode is used as the working electrode, the reference electrode is the silver/silver chloride electrode, the platinum sheet is used as the counter electrode, the ammonia content is measured with ion chromatography and indophenol blue spectrophotometry.

FIG. 4 is a test of hydrophilicity and hydrophobicity of the titanium carbide material prepared in example 1. As can be seen from the figure, the contact angle of water reaches 146 degrees, exhibiting superhydrophobicity.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. An in-situ alumina coated titanium carbide catalyst is characterized in that: the catalyst is sodium fluoride NaF and commercial titanium aluminum carbide Ti₃AlC₂The N-methylpyrrolidone NMP, sodium carbonate, sodium hydroxide and polytetrafluoroethylene PTFE are used as raw materials and are prepared by batch feeding and a heating and stirring method under mild conditions.

2. A method of preparing the in situ alumina coated titanium carbide catalyst of claim 1, wherein: etching and dissolving an Al layer in the titanium aluminum carbide by using sodium fluoride, filling the space of the Al layer with N-methyl pyrrolidone to form layered titanium carbide, and adjusting the pH value of a reaction system by using sodium carbonate and sodium hydroxide to convert dissolved Al ions into an aluminum oxide coating layer on the surface of the titanium carbide; meanwhile, the polytetrafluoroethylene emulsion is introduced to enable the polytetrafluoroethylene and the alumina layer to form close compounding, and therefore the super-hydrophobic in-situ alumina coated titanium carbide catalyst is finally obtained.

3. The method of claim 2, wherein: the method specifically comprises the following steps:

1) take 0.4 g Ti₃AlC₂And 50 mL of NMP solution containing 6 mol/LNaF are put into a plastic reactor and stirred and heated for reaction;

2) adding 0.05-0.2 g of sodium carbonate and 50-100 muL of PTFE emulsion with the content of 40wt% into the suspension obtained by the reaction, adjusting the pH value to 10 by using 4 mol/L of sodium hydroxide solution, continuing stirring for reaction, and then carrying out ultrasonic reaction for 1 h;

3) centrifuging the reaction solution in a centrifugal machine of 3500 r/min to remove the solvent, washing with anhydrous ethanol and deionized water respectively until the ion solubility of the solution is lower than 10ppm, and freeze-drying in a freeze dryer at-18 deg.C for 6h to obtain the sample.

4. The production method according to claim 3, characterized in that: the stirring and heating reaction in the step 1) is specifically as follows: stirring and heating at 60-100 deg.C at 1000 r/min for 1-4 h.

5. The production method according to claim 3, characterized in that: the step 2) of continuously stirring the reaction specifically comprises the following steps: the reaction is continued to be stirred for 0.5 to 2 hours at the temperature of 60 ℃ and the speed of 1000 r/min.

6. The production method according to claim 3, characterized in that: the ultrasonic machine conditions of the ultrasonic reaction in the step 2) are as follows: frequency 40 kHz, power 100W.

7. Use of the in situ alumina-coated titanium carbide catalyst of claim 1 for the electrochemical synthesis of ammonia.

8. Use according to claim 7, characterized in that: dispersing 2 mg of the catalyst in a dispersion liquid consisting of 225 muL ethanol, 225 muL water and 50 muL nafion, and after one hour of ultrasonic dispersion, taking 50 muL dispersed liquid drops in 1 x 1cm^-2The working electrode is made on the carbon paper, and then the traditional three-electrode system is used for electrocatalytic synthesis of ammonia.