CN115970540A - Preparation method of active carbon composite material loaded with nano metal or metal oxide - Google Patents
Preparation method of active carbon composite material loaded with nano metal or metal oxide Download PDFInfo
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Abstract
The invention discloses a high-efficiency preparation method of high-activity and high-surface-area active carbon for supporting nano-sized metal or metal oxide, which comprises the steps of mixing a metal compound solution with active carbon solution to enable a metal compound to be attached to the surface of the active carbon in an adsorption process, and heating and decomposing the metal compound; a process of making the metal compound adsorbed on the activated carbon by the adsorption process; the heating decomposition process is carried out in supercritical carbon dioxide, or microwave heating is adopted under atmospheric pressure; finally obtaining the active carbon composite material carrying the nano metal or the metal oxide.
Description
Technical Field
The present invention relates to a method for efficiently producing a nanometal or metal oxide-supported activated carbon suitable for use in a high-performance catalyst (catalyst), a supercapacitor, and an electrode of a fuel cell.
Background
The carbon material supported on the nano metal or the metal oxide can be applied as a catalyst, has a good conductive performance, and has attracted attention in recent years as an electrode material for a supercapacitor, a fuel cell, or the like. In particular, when the substrate is activated carbon, a large amount of nanoscale metal or metal oxide can be supported due to its characteristics such as high specific surface area and developed pores, and the activated carbon having high specific surface area can further improve the activity of the metal or metal oxide. The metal compound solution is usually mixed with activated carbon for adsorption, and then the mixture is dried and heated to decompose the metal compound into a metal or a metal oxide.
According to Lui et al (non-patent documents 1 and 2), spherical carbon black (XC-72, BET specific surface area: 220 to 250 m) is added to ethylene glycol 2 And/g) and chloroplatinic acid or ruthenium chloride aqueous solution, and heating by microwave after ultrasonic mixing to prepare the platinum and shackle carbon composite material.
According to Deborah L.et al (non-patent document 3), powdered carbon black (XC-72R, BET specific surface area: 250 to 300 m) 2 /g) mixing with acetone or aqueous solution of halogenated compound of platinum or palladium, drying, microwave heating the powder mixture in reducing atmosphere such as hydrogen, etc., and decomposing noble metal compound to prepare platinum and palladium carbon nano composite material. In addition, it has also been proposed to introduce a metal compound precursor into a porous body by using supercritical carbon dioxideA method of supporting a nano metal on carbon by heating inside pores of a carbon material (patent document 1).
[ Nonpatent document 1 ] Lui Z et al, langmuir,2004,20,181-187.
[ Nonpatent document 2 ] Lui Z et al, chem. Commun.2002,2588-2589.
[ non-patent document 3 ] Deborah L et al, chem. Mater.2001,13,806-810.
[ patent document 1 ] Japanese patent laid-open No. 2003-88756.
However, in the production methods of the above-mentioned non-patent documents 1 to 3, the method of adsorbing the metal compound on the powdered carbon by uniformly mixing with ultrasonic waves and merely performing the adsorption treatment by solution impregnation is suitable for a low-surface-area carbon black having no pores, but the high-surface-area activated carbon has a large number of micropores and the metal compound is difficult to smoothly enter the micropores, and therefore, the method is not suitable for producing a high-surface-area activated carbon composite of a metal or a metal oxide. In addition, in this solution adsorption method, in order to suppress the crystallization of the metal to a small extent, it is necessary to use a solvent of 400 times or more the solid content (the sum of carbon, metal compound, and the like), and therefore this method cannot be said to be an efficient method.
Further, patent document 1 discloses that a metal compound precursor is dissolved in supercritical carbon dioxide, inserted into pores of a porous carbon material, dispersed and supported on the surface of the carbon material, and can support fine metal particles. In this method, a metal compound solution is placed in the lower part of a pressure vessel, activated carbon is placed in the upper part, supercritical carbon dioxide is fed, a precursor is adsorbed in the pores of the activated carbon under a gas-liquid equilibrium, and the precursor is heated and decomposed to cause the metal to be supported on the activated carbon. Since the metal compound is not in direct contact with the carbon material, a long-term high-temperature high-pressure treatment is required to increase the amount of the metal supported. In addition, in this method, there is a concern that crystals of the metal compound may grow with evaporation of the solvent in the filtration and drying steps, and in the ordinary heat baking method, it takes a long time to reach the target temperature, and therefore there is a problem that it is difficult to prevent crystal growth, secondary aggregation, and the like.
Disclosure of Invention
In order to realize the technical problem, the invention provides a high-efficiency preparation method of a high-activity and high-surface-area active carbon composite material loaded with nano metal or metal oxide, which is suitable for high-performance catalysts, super capacitors or fuel cell electrode materials. The technical scheme for solving the technical problems is as follows:
a preparation method of an active carbon composite material carrying nano metal or metal oxide comprises the steps of dissolving one or more metal compounds in one or more solvents, adding active carbon, uniformly mixing, and carrying out reduced pressure degassing treatment while stirring to obtain a mixture A; placing the mixture A in a high-pressure container, stirring in supercritical carbon dioxide of 30MPa or below and 200 ℃ or below, and performing adsorption treatment for less than 2h to obtain a mixture B; maintaining the pressure in supercritical carbon dioxide atmosphere, adjusting the temperature to 300 deg.C or below, performing thermal decomposition reaction within 30min, reducing pressure, cooling to room temperature, cleaning, filtering, and drying to obtain the metal or metal oxide-loaded active carbon composite material.
Preferably, the BET specific surface area of the activated carbon is 1000m 2 (ii) at least one of the activated carbon and the activated carbon is in the form of powder or fiber.
Preferably, the BET specific surface area of the activated carbon is 2000m 2 More than g.
Preferably, the metal compound is a compound of platinum (Pt), palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru), titanium (Ti).
Preferably, the solvent is acetone, ethanol, methanol, ethylene glycol or water.
Preferably, the weight ratio of the solvent to the total amount of the activated carbon and the metal compound is 10 to 100:1, the weight of the active carbon and the metal compound is 1-10: 1.
preferably, the weight ratio of the solvent to the total amount of the activated carbon and the metal compound is 30-60: 1.
preferably, 0.5 to 1mL of 2M alkaline solution is added simultaneously with the addition of the activated carbon, and the metal compound can be decomposed into a metal or a metal oxide at a relatively low temperature in the thermal decomposition process.
The preparation method of the active carbon composite material loaded with the nano metal or the metal oxide is based on the preparation method, the mixture B is prepared by adopting a high boiling point solvent, the mixture B is cooled and decompressed and taken out, and then is arranged in a microwave heating device in a solvent-containing state for heating decomposition, the heating temperature is 300 ℃ or below, and the heating time is within 5min, so that the active carbon composite material loaded with the metal or the metal oxide is obtained.
The preparation method of the active carbon composite material loaded with the nano metal or the metal oxide is based on the preparation method, the mixture B is prepared by adopting a low-boiling-point solvent, the mixture B is decompressed and cooled, then the mixture B is filtered and dried to obtain a powdery mixture B, and the powdery mixture B is heated by adopting microwaves under the atmospheric pressure, wherein the heating temperature is 300 ℃ or below, and the heating time is within 10min, so that the active carbon composite material loaded with the metal or the metal oxide is obtained.
Compared with the prior art, the invention has the beneficial effects that:
the invention discloses a high-efficiency preparation method of a high-activity and high-surface-area active carbon composite material which is suitable for a high-performance catalyst, a super capacitor or a fuel cell electrode material and carries nano metal or metal oxide. According to the production method of the present invention, the supported amount of the metal or the metal oxide is high, and the metal or the metal oxide of several nanometers can be uniformly supported on the surface of the micropores of the activated carbon. As the adsorption method, the metal compound solution and the activated carbon are mixed and stirred in the supercritical carbon dioxide, whereby the metal compound can be adsorbed on the activated carbon in a short time and with high efficiency without leaving a residue.
The thermal decomposition process of the metal compound adsorbed on the activated carbon in the present invention is carried out by two methods. The first method is to thermally decompose a metal compound in a supercritical state. The decomposition reaction proceeds while maintaining the state of adsorption in the supercritical fluid, and the metal or metal oxide can be more uniformly supported. Since the pyrolysis process and the adsorption process are performed in the same apparatus, the operation procedure is simplified. The second method is to perform thermal decomposition by microwave irradiation after adsorption treatment in a supercritical fluid. The active carbon material is a microwave absorber, so that the active carbon material can be rapidly heated and decomposed, the treatment time is greatly reduced, the growth and secondary agglomeration of crystals can be inhibited, and the loading of small-size nano metal or metal oxide particles on the active carbon can be realized.
Drawings
FIG. 1 is a schematic diagram of an apparatus for adsorption using supercritical carbon dioxide;
FIG. 2 is a TEM photograph of the metal-supported activated carbon composite obtained in example 1;
FIG. 3 is a TEM photograph of the metal-supported activated carbon composite obtained in example 3;
FIG. 4 is an X-ray diffraction pattern of the metal-supported activated carbon composite materials obtained in examples 1, 2, 4 and 8;
FIG. 5 is an X-ray diffraction chart of the metal-supporting activated carbon composite materials obtained in examples 9 and 10;
FIG. 6 is an X-ray diffraction chart of the metal-supporting activated carbon composite materials obtained in comparative examples 1 to 4.
Reference numerals: 1. the method comprises the following steps of mixing raw materials, 2. A Teflon container, 3. A high-pressure container, 4. A stirring wing, 5. A motor, 6. A thermocouple thermometer, 7. A thermometer, 8. A pressure gauge, 9. A heater and 10. A high-pressure pump.
Detailed Description
The following description of the embodiments of the present invention will be described in further detail with reference to the accompanying drawings, but the embodiments are not intended to limit the present invention, and all similar combinations and similar variations using the present invention shall fall within the scope of the present invention.
The method comprises the following steps:
in order to achieve a metal loading ratio of 5 to 30wt%, a predetermined amount of a metal compound is dissolved in a predetermined amount of a solvent, uniformly mixed with a predetermined amount of activated carbon, and then subjected to a vacuum degassing treatment for 30 minutes or more while stirring to obtain a mixture A. The amount of the solvent is 10 to 100 times, preferably 30 to 60 times the total solid content of the activated carbon, the metal compound and the like.
Placing the mixture in a high pressure vessel, introducing carbon dioxide under pressure, and performing adsorption treatment in supercritical carbon dioxide under 30MPa and below 200 deg.C and below the decomposition temperature of metal compound for 2 hr while stirring to obtain mixture B.
Preparation method 1:
and (2) maintaining the pressure of the mixture B obtained in the step one in a supercritical carbon dioxide atmosphere, adjusting the temperature to be below 300 ℃, decomposing the metal compound within 30 minutes, cooling, reducing the pressure, taking out the mixed material, cleaning, filtering and drying to obtain the active carbon composite material carrying the nano metal or the metal oxide.
The preparation method comprises the following steps:
cooling and depressurizing the mixture B obtained in the first step, taking out, placing the mixture B in a microwave heating device in a state of containing a solvent when a high-boiling-point solvent is used, and heating the mixture B at an optimal temperature of less than 300 ℃ for 5 minutes while stirring the mixture B under microwave irradiation to decompose the metal compound adsorbed on the activated carbon into a metal or a metal oxide. In this case, since a treatment such as drying is not performed before the heating treatment, the metal compound adsorbed on the pore surface of the activated carbon can prevent crystal precipitation and growth due to evaporation of the solvent, and thus a composite material in which the nano metal particles or nano oxide particles are uniformly dispersed on the surface of the activated carbon can be obtained. In addition, the activated carbon is a microwave absorber, and can be rapidly heated by microwave irradiation, so that the heating time can be greatly reduced, and further, the growth and secondary agglomeration of crystals can be inhibited.
The preparation method comprises the following steps:
cooling and depressurizing the mixture B obtained in the first step, taking out the mixture B under the condition of using a low-boiling point solvent, filtering and drying the mixture B, removing the solvent, placing the powdery mixture in a microwave heating device, and carrying out microwave heating at an optimal temperature of below 300 ℃ to decompose the metal compound adsorbed on the activated carbon into metal or metal oxide. The heating time is 10 minutes or less, the thermal decomposition time can be greatly reduced, and the growth and secondary aggregation of crystals can be suppressed.
The present invention is not limited to the above-described production method, and variations and modifications within a range that can achieve the object of the present invention are included in the present invention. For example, in the above-mentioned production method 1, the pressure of the thermal decomposition process of the adsorbed mixture in the supercritical carbon dioxide atmosphere may be changed depending on the adsorption treatment process. In the above-mentioned production methods 2 and 3, it is proposed that the thermal decomposition temperature by microwave heating is 300 ℃ or lower and the treatment time is 10 minutes or less, but the heating treatment may be carried out at 300 ℃ or higher and 10 minutes or longer. In addition, the frequency of the microwave is not limited to 2.45GHz.
The BET specific surface area of the raw material activated carbon used in the present invention was 1000m 2 A ratio of at least 2000 m/g, preferably 2 The specific surface area of the activated carbon is more than g. The shape of the activated carbon may be powder or fiber. In addition, as the metal compound, a noble metal compound is preferably used. For example, platinum (Pt), palladium (Pd), gold (Au), silver (Ag), or the like can be used alone or in combination. Examples of the metal or metal oxide supported on the activated carbon include platinum-palladium (Pt-Pd), platinum-ruthenium (Pt-Ru), platinum-ruthenium oxide (Pt-RuOx), and silver-titanium oxide (Ag-TiO) 2 ) And the like.
As the solvent, a solvent capable of dissolving the metal compound may be used. Acetone, ethanol, methanol, water, ethylene glycol, etc. may be used, but it is necessary to select an optimum solvent according to the metal compound. For example, when chloroplatinic acid is used and decomposed in supercritical carbon dioxide, platinum particles having the best acetone and the smallest particle size are obtained. In addition, when thermal decomposition is performed by microwave irradiation, ethylene glycol having a high boiling point is preferably used.
In the raw material mixing step of the present invention, one or more metal compounds are dissolved in one or more mixed solvents, and the resulting solution is uniformly mixed with activated carbon, and then subjected to pressure reduction treatment while stirring to allow the metal compounds to permeate into the activated carbon.
In addition, the present inventors have discovered that metal compounds can be decomposed to metals or metal oxides at lower temperatures by adding a small amount of an alkaline solution during the mixing of the metal compound solution and the high surface area activated carbon. As the base, potassium hydroxide, sodium hydroxide, or the like can be used, but not limited thereto.
In the supercritical carbon dioxide adsorption process of the present invention, the mixed raw material 1 is placed in a teflon vessel 2 and placed in a high-pressure vessel 3 using a reaction apparatus shown in fig. 1. The reaction device is respectively provided with a stirring wing 4, a motor 5, a thermocouple thermometer 6, a thermometer 7 and a pressure gauge 8 for reaction. After replacing the air in the container with carbon dioxide, the pressure, temperature and time of the stirring treatment are adjusted to the desired values by the high-pressure pump 10 and the heater 9. The treatment pressure, temperature and time vary depending on the type and amount of the metal compound, the type of the solvent and the characteristics of the activated carbon, and it is preferable that the pressure is 30MPa or less, the temperature is 200 ℃ or less and the time is 2 hours or less. For example, when platinum is supported, chloroplatinic acid (H) is used 2 PtCl 6 ·6H 2 O) as a metal compound, using acetone or ethylene glycol as a solvent, and treating the mixture at a pressure of 20MPa of supercritical carbon dioxide and a temperature of 100 ℃ for 1 hour to achieve an adsorption rate of the platinum compound of 99wt% or more. The average particle diameter of the metal platinum particles in the composite material after the thermal decomposition is 5nm or less.
In the present invention, the thermal decomposition process of converting the metal compound adsorbed on the activated carbon into metal particles or metal oxide particles in the supercritical carbon dioxide atmosphere is carried out in two atmospheres.
The method 1 is a method in which after adsorption treatment is performed in a supercritical carbon dioxide atmosphere for a predetermined period of time, the temperature is raised to a predetermined temperature under a predetermined pressure in the same apparatus, and a metal compound is thermally decomposed for a predetermined period of time.
In the 2 nd method, after the metal compound is adsorbed in supercritical carbon dioxide, the mixture is returned to normal temperature and pressure, and the treated mixture is taken out, transferred to a container in a microwave heating apparatus, and subjected to thermal decomposition by microwave irradiation under atmospheric pressure. The treatment process varies depending on the solvent used, and when the boiling point of the solvent is higher than the thermal decomposition temperature of the metal, the solvent is placed in a microwave heating device in a state of being mixed with the solvent, and the material is heated at a predetermined temperature for a predetermined time while being stirred, so that the metal compound adsorbed on the activated carbon is thermally decomposed into the metal or the metal oxide; when the boiling point of the solvent is lower than the temperature of the metal compound, the mixture after adsorption treatment is taken out from the pressure vessel, filtered and dried, and the obtained powdery mixture is arranged in a microwave heating device and heated at a predetermined temperature for a predetermined time to thermally decompose the metal compound into metal or metal oxide. The activated carbon material is a microwave absorber, and is rapidly heated by microwave irradiation, so that the heating time can be greatly reduced, and the growth and secondary aggregation of crystals can be suppressed.
The mixture after the thermal decomposition is washed with pure water or the like, filtered, and dried to obtain an activated carbon composite material carrying a nano metal or a metal oxide.
The preparation method of the metal or metal oxide supported active carbon composite material has the following effects:
(1) In the present invention, since the high surface area activated carbon is used, the amount of the metal or metal oxide to be supported and the area to be supported can be increased.
(2) In the adsorption process, the mixture of the metal compound solution and the activated carbon is treated in the supercritical carbon dioxide while being stirred, so that the metal compound can be efficiently adsorbed on the activated carbon in a short time without remaining in the solvent. Therefore, the loading rate can be controlled by the raw material mixing ratio.
(3) In the thermal decomposition process, when the metal compound is thermally decomposed in a supercritical state, the activated carbon and the metal compound adsorbed on the surface of the pore can be decomposed in a state of equilibrium in the atmosphere, and the nano metal particles or nano metal oxide particles can be uniformly supported. In addition, since the pyrolysis is performed using the same apparatus as the adsorption process, the manufacturing process can be simplified.
(4) When the adsorbed metal compound is thermally decomposed, microwave heating is used, and since activated carbon is an excellent microwave absorber, rapid heating is possible, and the treatment time is significantly shortened. In addition, the local rapid heating can suppress the growth of crystals and secondary aggregation, and smaller metal particles or metal oxide particles can be supported on the activated carbon.
In order to understand the present invention, materials used in examples and comparative examples will be described. The supercritical fluid is carbon dioxide with purity of 99.99%, acetone, ethanol, methanol, deionized water, ethylene glycol, etc. Further, FCO-30S (BET specific surface area: about 3500 m) manufactured by Apolesch energy Corp, zhejiang was used as the high surface area activated carbon material 2 Per gram) activated carbon; as the metal precursor, chloroplatinic acid hexahydrate (H) was used 2 PtCl 6 ·6H 2 O), platinum potassium tetrachloroate (K) 2 PtCl 4 ) Ruthenium trichloride (RuCl) 3 ) And the like. The following are 10 examples of the present invention, specifically as follows:
example 1
In order to achieve a platinum loading rate of 10wt%, 0.27g of platinum hexachloride hexahydrate was dissolved in 100ml of ethylene glycol, 1g of activated carbon was added, and the mixture was degassed under reduced pressure while stirring, and the obtained mixture was placed in a high-pressure vessel and subjected to adsorption treatment for 1 hour while stirring in 20MPa, 100 ℃ supercritical carbon dioxide. Then, the temperature was raised to 185 ℃ while maintaining the system pressure at 20MPa, and then the sample was cooled to room temperature while reducing the pressure. And washing the mixture by using deionized water after filtration, and drying the mixture for 2 hours at 120 ℃ to obtain the platinum particle-loaded activated carbon composite material. The specific surface area of the obtained material, the adsorption rate of the platinum compound, and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 1. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 4. As a result, the utilization rate of platinum was high, and it was 99.9%, and the particle diameter of platinum was 5nm or less.
Example 2
When the solution in which the metal compound was dissolved was mixed with activated carbon, 0.5M and 2M aqueous potassium hydroxide (KOH) solution was added to the mixture, and adsorption and thermal decomposition processes were performed in the same manner as in example 1. The temperature for thermal decomposition was set at 135 ℃. The specific surface area of the obtained material, the adsorption rate of the platinum compound, and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 1. Further, a TEM photograph of the composite material is shown in FIG. 2, and an X-ray diffraction pattern is shown in FIG. 4. The results show that the utilization rate of platinum is high, and is 99.8%. Further, it was found that platinum had a particle size of 5nm or less and was uniformly distributed on the surface of the pores of the activated carbon.
Example 3
The mixture was subjected to adsorption treatment in the supercritical fluid in the same manner as in example 1, cooled, depressurized, and taken out, and then placed in a microwave heating apparatus in a state of containing a solvent. The temperature was raised to 185 ℃ over 2 minutes while stirring, and held for 1 minute. And cooling to room temperature, filtering, washing with deionized water, and drying at 120 ℃ for 2 hours to obtain the platinum-loaded active carbon composite material. The specific surface area of the obtained material, the adsorption rate of the platinum compound, and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 1. The results showed that the utilization of platinum was high, 99.8%, and the particle size of platinum particles was about 5nm.
Example 4
When the metal compound was mixed with the solvent and activated carbon, 0.5ml of 2M aqueous potassium hydroxide solution was added to the mixture. Other treatments were carried out by adsorption and thermal decomposition under the same conditions as in example 3. However, the thermal decomposition temperature of the microwave heating was set at 135 ℃. The specific surface area of the obtained material, the adsorption rate of the platinum compound, and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 1. Further, a TEM photograph of the composite material is shown in FIG. 3, and an X-ray diffraction pattern is shown in FIG. 4. The results showed that the utilization rate of platinum was 99.9%, the particle size of platinum was 5nm or less, and the platinum was uniformly distributed on the surface of the pores of the activated carbon.
Example 5
After 0.25g of chloroplatinic acid hexahydrate was dissolved in 8ml of acetone, 1g of activated carbon was added thereto, and the mixture was degassed under reduced pressure while being stirred. The resulting mixture was placed in a high-pressure vessel, and subjected to adsorption treatment for 1 hour while being stirred in supercritical carbon dioxide at 100 ℃ under 20 MPa. Subsequently, the pressure of the system was maintained at 20MPa, the temperature was raised to 185 ℃ and then cooled to room temperature while reducing the pressure, and the sample was taken out. Filtering, washing, and drying at 120 deg.C for 2 hr to obtain the active carbon composite material carrying platinum. The specific surface area of the obtained material, the adsorption rate of the platinum compound, and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 1. The results showed that the utilization of platinum was 90% and the particle size of platinum was around 5nm.
Example 6
The mixture was mixed by the same method as in example 5, and the mixture was adsorbed by supercritical adsorption, cooled and depressurized, and then the sample was taken out, filtered and dried, and the obtained powdery material was placed in a microwave heating apparatus, and the temperature was raised to 185 ℃ within 2 minutes, and held for 1 minute. Then, after cooling to room temperature, washed with deionized water and filtered. Drying at 120 ℃ for 2 hours to obtain the activated carbon composite material loaded with platinum particles. The adsorption rate of the platinum compound and the average particle diameter of the platinum particles supported on the activated carbon of the obtained material are shown in table 1. Substantially the same results as in example 5 were obtained.
Example 7
To achieve a platinum loading rate of 30wt%, 0.4g of chloroplatinic acid hexahydrate was dissolved in 100ml of ethylene glycol, 0.5g of activated carbon was added, and degassing was performed by vacuum-pumping while stirring. The obtained mixture was placed in a high-pressure vessel, and subjected to adsorption treatment for 1 hour while being stirred in supercritical carbon dioxide at 100 ℃ under 20 MPa. Subsequently, the temperature was raised to 185 ℃ while maintaining the system pressure at 20MPa, and then the sample was cooled to room temperature while reducing the pressure, and after filtering, the sample was washed with deionized water and dried at 120 ℃ for 2 hours to obtain a platinum-carrying activated carbon composite material. The specific surface area of the obtained material, the adsorption rate of the platinum compound, and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 1. The results showed that the platinum utilization rate was as high as 99.9% even when the platinum loading rate was increased. The particle diameter of platinum is 5nm or less.
Example 8
After the mixture was degassed in the same manner as in example 1, the mixture was stirred at room temperature for 24 hours, and then placed in a microwave heating apparatus, and the temperature was raised to 185 ℃ for 2 minutes while stirring, and the mixture was held for 1 minute. And cooling to room temperature, filtering, washing with deionized water, and drying at 120 ℃ for 2 hours to obtain the platinum-loaded active carbon composite material. The adsorption rate of the platinum compound of the obtained material and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 1. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 4. The results show that substantially the same results can be obtained if the mixing is carried out by stirring for a long time without carrying out the supercritical adsorption.
Example 9
In order to achieve a ruthenium loading rate of 5wt%, 0.1g of ruthenium trichloride was dissolved in 100ml of ethylene glycol, and then 1g of activated carbon was added, followed by degassing treatment by vacuum-pumping while stirring. The obtained mixture was placed in a high-pressure vessel, and subjected to adsorption treatment for 1 hour while being stirred in supercritical carbon dioxide at 20MPa and 100 ℃. Subsequently, the temperature was raised to 185 ℃ while maintaining the system pressure at 20MPa, and then the sample was cooled to room temperature while reducing the pressure, and then the sample was taken out, filtered, washed with deionized water, and dried at 120 ℃ for 2 hours to obtain a ruthenium-supported activated carbon composite material. The adsorption rate of the ruthenium compound of the obtained material and the average particle diameter of the ruthenium particles supported on the activated carbon are shown in table 1. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 5. From the results, the yield of ruthenium was 97%, and the particle diameter of ruthenium was 5nm or less.
Example 10
After the mixing and the supercritical adsorption treatment were carried out in the same manner as in example 9, the sample was cooled and decompressed, taken out, set in a microwave heating apparatus in a state of containing a solvent, and heated to 185 ℃ over 2 minutes while stirring, and held for 1 minute. And cooling to room temperature, filtering, washing with deionized water, and drying at 120 ℃ for 2 hours to obtain the ruthenium-loaded active carbon composite material. The specific surface area of the obtained material, the adsorption rate of the ruthenium compound, and the average particle diameter of the ruthenium particles supported on the activated carbon are shown in table 1. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 5. The results showed that the yield of ruthenium was 97% and the particle size of ruthenium was 5nm or less.
TABLE 1
Table 1 shows the specific surface area, the adsorption rate of the metal precursor compound, and the average particle diameter of the metal particles supported on the activated carbon, of the metal-supported activated carbon materials obtained in examples 1 to 10.
Comparative example 1
The solvent was used in the same manner as in example 6, except that methanol was used instead of acetone. The specific surface area, the platinum compound adsorption rate, and the average particle diameter of the platinum particles supported on the activated carbon of the obtained material are shown in table 2. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 6. The results showed a platinum utilization of 93.7%. The particle size of platinum was 16.7nm, which is slightly larger.
Comparative example 2
The solvent was used in the same manner as in example 6, except that ethanol was used instead of acetone. The specific surface area, the platinum compound adsorption rate, and the average particle diameter of the platinum particles supported on the activated carbon of the obtained material are shown in table 2. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 6. The results showed that the utilization of platinum was slightly low, 85%, and the particle size of platinum was 8.5nm.
Comparative example 3
The solvent was used in the same manner as in example 6, except that water was used instead of acetone. The specific surface area, the platinum compound adsorption rate, and the average particle diameter of the platinum particles supported on the activated carbon of the obtained material are shown in table 2. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 6. The results showed that the utilization of platinum was low at 77.1%, and the particle size of platinum was large at 16.1nm.
Comparative example 4
0.27g of chloroplatinic acid hydrate was dissolved in 8ml of water, 1g of activated carbon was added, and after degassing treatment by evacuation with stirring, further mixing treatment was carried out for 15 minutes with ultrasonic waves, and then the mixture was set in a microwave heating apparatus, and heated to 185 ℃ for 2 minutes while stirring, and held for 1 minute. Cooling to room temperature, filtering, washing with deionized water, and drying at 120 ℃ for 2 hours to obtain the platinum-loaded active carbon composite material. The specific surface area of the obtained material, the adsorption rate of the platinum compound, and the average particle diameter of the platinum particles supported on the activated carbon are shown in table 2. In addition, the X-ray diffraction pattern of the composite material is shown in fig. 6. The results showed that the utilization rate of platinum was as low as 34%, and the particle size of platinum was as large as 13nm or more.
TABLE 2
Table 2 shows the specific surface area of the metal-loaded activated carbon material, the adsorption rate of the metal precursor compound, and the average particle diameter of the metal particles loaded on the activated carbon obtained in comparative examples 1 to 4.
Possibility of industrial application:
carbon composite materials carrying nano metals and metal oxides are widely used as electrode materials for catalysts, fuel cells, supercapacitors and the like. However, the general solution impregnation method is only applicable to a carbon material having a low specific surface area without pores such as carbon black. Further, in order to suppress the crystallization of the metal to a small extent, it is necessary to use a large amount of solvent of 400 times or more as large as the solid matter (sum of carbon, metal compound and the like), and therefore, it cannot be said that this method is an efficient method. In the conventional production method using supercritical carbon dioxide, the amount of metal to be supported is difficult to control, and in order to increase the amount of metal to be supported, a long-term treatment at high temperature and high pressure is required. Not only consumes a large amount of energy, but also has low production efficiency. In addition, in the filtration and drying process of this method, there is a possibility that crystals of the metal compound grow as the solvent evaporates. In the thermal decomposition process, a long heating time is required to reach a target temperature by ordinary heating, and it is difficult to prevent crystal growth and secondary aggregation. However, in the present invention, the high surface area activated carbon and the metal precursor compound are directly mixed in the supercritical carbon dioxide and stirred during the treatment, whereby the adsorption can be more effectively performed and the predetermined target loading rate can be achieved. In addition, in the thermal decomposition process, thermal decomposition performed in a supercritical state is performed in the same apparatus as the adsorption treatment, and thus the production steps can be simplified. On the other hand, by using microwave heating, not only the time for the thermal decomposition treatment can be significantly reduced, but also the growth and secondary aggregation of crystals can be suppressed. Smaller sized metals or metal oxides may be supported on the activated carbon. Therefore, the preparation method of the invention is more suitable for preparing the high-surface-area activated carbon composite material loaded with nano metal or metal oxide. In addition, since the product of the present invention can be efficiently produced in a short time, the product and the process for producing the same are considered to be widely applicable.
The above description is only an embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that are not thought of through the inventive work should be included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope defined by the claims.
Claims (10)
1. A method for preparing an active carbon composite material loaded with nano metal or metal oxide is characterized by comprising the following steps: dissolving one or more than one metal compound in one or more than one solvent, adding active carbon, uniformly mixing, and carrying out reduced pressure degassing treatment while stirring to obtain a mixture A; placing the mixture A in a high-pressure container, stirring in supercritical carbon dioxide of 30MPa or below at 200 deg.C or below for adsorption treatment for 2 hr to obtain mixture B; maintaining the pressure in supercritical carbon dioxide atmosphere, adjusting the temperature to 300 deg.C or below, performing thermal decomposition reaction within 30min, reducing pressure, cooling to room temperature, cleaning, filtering, and drying to obtain the metal or metal oxide-loaded active carbon composite material.
2. The method of claim 1, wherein: the BET specific surface area of the activated carbon is 1000m 2 More than/g, the shape of the activated carbon is powder or fiber.
3. The method of claim 2, wherein: the BET specific surface area of the activated carbon is 2000m 2 More than g.
4. The production method according to claim 3, characterized in that: the metal compound is a compound of platinum (Pt), palladium (Pd), gold (Au), silver (Ag), ruthenium (Ru) and titanium (Ti).
5. The method of claim 4, wherein: the solvent is acetone, ethanol, methanol, glycol or water.
6. The method of claim 5, wherein: the weight ratio of the solvent to the total amount of the activated carbon and the metal compound is 10 to 100:1, the weight of the activated carbon and the metal compound is 1 to 10:1.
7. the method of manufacturing according to claim 6, characterized in that: the weight ratio of the solvent to the total amount of the activated carbon and the metal compound is 30 to 60:1.
8. the method for producing according to claim 7, characterized in that: adding 0.5-1mL of 2M alkaline solution into the mixture during the process of adding the activated carbon, and decomposing the metal compound into metal or metal oxide at a lower temperature during the heating decomposition process.
9. The production method according to any one of claims 1 to 8, characterized in that: and the mixture B is prepared by adopting a high-boiling-point solvent, is cooled, decompressed and taken out, and is arranged in a microwave heating device to be heated and decomposed in a solvent-containing state, the heating temperature is 300 ℃ or below, and the heating time is within 5min, so that the metal or metal oxide-loaded active carbon composite material is obtained.
10. The production method according to any one of claims 1 to 8, characterized in that: the mixture B is prepared by adopting a low-boiling-point solvent, the mixture B is decompressed and cooled, then the mixture B is filtered and dried to obtain a powdery mixture B, and the powdery mixture B is heated by adopting microwaves under atmospheric pressure, the heating temperature is 300 ℃ or below, and the heating time is within 10min, so that the metal or metal oxide supported active carbon composite material is obtained.
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