CN109772465B - Preparation method of water-soluble carbon dot modified perovskite type catalytic material - Google Patents
Preparation method of water-soluble carbon dot modified perovskite type catalytic material Download PDFInfo
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Abstract
The invention relates to a preparation method of a water-soluble carbon point modified perovskite type catalytic material, which comprises the following steps of 1, mixing amino acid, alcohol and urea or citric acid according to a proportion, and uniformly stirring until a transparent eutectic solvent is formed; 2, weighing perovskite metal precursor, fuel and fuel additive, mixing, stirring and stirring to obtain precursor mixed solution, and roasting at 650-850 ℃ for 3-6h to obtain perovskite metal oxide catalyst; 3 mixing the transparent eutectic solvent and the perovskite metal oxide catalyst with deionized water; 4 reacting at the temperature of 180 ℃ and 230 ℃ for 3-7 h; 5, cooling, washing and filtering; 6 drying at 80 ℃, and then roasting at 600 ℃ for 1-3 h. According to the invention, the physicochemical properties of the surface of the perovskite type catalytic material are optimized by adding the carbon-containing precursors, namely amino acid, alcohol and urea or citric acid, and the prepared modified perovskite type catalytic material can catalyze and degrade methane more efficiently.
Description
Technical Field
The invention belongs to the technical field of chemical industry, environmental protection and catalytic materials, and particularly relates to a preparation method of a modified perovskite type catalytic material.
Background
The organic matter is the main component of urban environment particulate matter, and is also PM and O3Important precursors. Most of industrial emission series Volatile Organic Compounds (VOCs) have obvious ' three-cause ' effect, become toxic tumors affecting the health of residents, and are environment-friendly ' bottles for restricting the development of national economyNeck ". With the tightening of the discharge standards of VOCs in China, places and industries, the deep mineralization of VOCs becomes inevitable.
VOCs components are complex, gas velocity and concentration fluctuation are large, and a thermal, ultraviolet and plasma coupling catalyst purification technology becomes the first choice. The efficiency of thermally catalyzing and oxidizing VOCs is high, and VOCs can be deeply mineralized into CO2And H2O, effectively avoiding secondary pollution, but having large energy consumption and high operation cost; if the ring opening temperature of the benzene series is about 200 ℃, and the complete mineralization needs to reach more than 350 ℃. The high-efficiency catalyst becomes the key of the deep mineralization technology of the VOCs.
Perovskite catalysts are of increasing interest to more and more researchers due to their excellent redox properties, hydrothermal stability, and ultra-long life, among others, as compared to high cost precious metals. For example, replacing ABO with exogenous cations3The a or B sites of (a) are used to modulate catalyst surface oxygen vacancies, making them viable alternatives to platinum-based noble metal materials (PGMs) in many catalytic applications. However, the preparation of perovskite catalysts requires higher temperatures and longer calcination times, resulting in lower surface areas and less efficient surface catalytic reactions. In order to increase the surface area of the reactant interacting with the substrate, research on porous perovskites of different morphologies has been conducted, using a templating method to form an ordered porosity material to increase the active contact area of the reactant with the material. Although the introduction of ordered porosity can significantly improve the catalytic activity of the metal oxide, this synthesis process is complex and uneconomical; other perovskite materials prepared by various wet chemical reaction processes, such as coprecipitation treatment, sol-gel treatment and hydrothermal treatment, also have various disadvantages, such as difficulty in simultaneously controlling the precipitation of cations in a solution in the coprecipitation method, often resulting in the separation of components; sol-gel techniques typically use expensive metal alkoxides as raw materials; hydrothermal processes generally require long reaction times. Therefore, there is a need to further explore and develop simpler, cheaper perovskite composite metal oxide technologies.
Disclosure of Invention
The invention aims to provide a preparation method of a water-soluble carbon-point modified perovskite-type catalytic material, wherein the physicochemical property of the surface of the perovskite-type catalytic material is optimized by adding carbon-containing precursors, namely amino acid, alcohol and urea or citric acid, and the prepared modified perovskite-type catalytic material can catalyze and degrade methane more efficiently; the preparation method provided by the invention is simple and efficient.
In order to achieve the above object, the preparation method of the present invention comprises the steps of,
(1) mixing amino acid, alcohol and urea or citric acid according to a proportion, and uniformly stirring until a transparent eutectic solvent is formed; the amino acid: alcohols: the molar ratio of urea or citric acid is 1: (4-6): (1-5);
(2) weighing a perovskite metal precursor, a fuel and a fuel additive, wherein the perovskite metal precursor is two or more of rare earth metal nitrate, transition metal nitrate and alkaline earth metal nitrate; the fuel is one of urea, glycine, sucrose or citric acid; the fuel additive is one of ammonium acetate, starch or polyethylene glycol;
dissolving a perovskite metal precursor in deionized water, controlling the molar concentration of total metal ions in the solution to be 0.5-2.0 mol/L, and then adding fuel and a fuel additive; the sum of the fuel and the fuel additive is 1 to 2 times of the sum of the total metal ions added before; the molar ratio of the fuel to the fuel additive is (2-5): 1; stirring for 0.5h at room temperature to obtain a precursor mixed solution, and roasting the precursor mixed solution for 3-6h at 650-850 ℃ to obtain a perovskite metal oxide catalyst;
(3) mixing the transparent eutectic solvent obtained in the step (1) and the perovskite obtained in the step (2)
Mixing the ore metal oxide catalyst with deionized water, and adding the deionized water according to the proportion of 2-10mL of deionized water added into the perovskite metal oxide catalyst obtained in the step (2) per gram; the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1 (1-6);
(4) putting the product obtained in the step (3) into a reaction kettle, sealing and reacting for 3-7h at the temperature of 180-;
(5) naturally cooling, and alternately washing and filtering for 3-6 times by using ethanol and deionized water;
(6) and (4) drying the product obtained in the step (5) at 80 ℃, and then roasting for 1-3h at 600 ℃.
Further, in the step (1), the amino acid is selected from one of glycine, lysine, arginine, cysteine, threonine, serine or histidine.
Further, in the step (1), the alcohol is selected from one of ethylene glycol, glycerol, polyethylene glycol 200, polyethylene glycol 400 or polyethylene glycol 800.
Further, in step (1), the amino acid: alcohols: the molar ratio of urea or citric acid is 1: 6: 3.
further, in the step (2), it is characterized in that: the total metal ion molar concentration in the step (1) is 1 mol/L.
Further, in the step (2), it is characterized in that: the molar amount of the sum of the fuel and the fuel additive is 1.5 times the molar amount of the sum of all the metal ions added.
Further, in the step (2), it is characterized in that: the molar ratio of the fuel to the fuel additive is 4: 1.
further, in the step (3), the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1: 2.
Further, in the step (4), the reaction temperature is 200 ℃ and the reaction time is 4 h.
Further, in the step (6), the product is dried at 80 ℃, heated to 600 ℃ at 3 ℃/min and then roasted at 600 ℃ for 1 h.
The invention has the following positive effects:
the preparation method is simple, adopts non-noble metal oxide as the main synthetic material of the catalyst, and has low cost.
According to the invention, the carbon point modified perovskite catalytic material is carried out through the eutectic solvent of amino acids, so that the surface water solubility of the perovskite is increasedThe physical and chemical properties of the surface of the modified surface are modified by the sexual groups, namely carboxyl, hydroxyl and amide; meanwhile, the catalyst is subjected to secondary crystallization through hydrothermal treatment, the particle agglomeration phenomenon caused by high-temperature roasting is improved, the particle enlargement of the perovskite metal oxide catalyst is inhibited, more active sites are exposed on the material, and the methane catalytic degradation performance of the perovskite metal oxide catalyst is improved. Compared with the existing perovskite catalyst, the carbon dot/perovskite composite methane catalyst obtained by the invention has the advantages that the methane T is50%The temperature is reduced by about 100 ℃.
Drawings
FIG. 1 is an activity test profile of the product of example 1;
FIG. 2 is an activity test profile of the product of example 2;
FIG. 3 is an XRD pattern of the product of example 1;
FIG. 4 is an XRD pattern of the product of example 2;
FIG. 5 is the FT-IR spectrum of the product of example 1;
FIG. 6 is the FT-IR spectrum of the product of example 2.
Detailed Description
Example 1
The embodiment provides a preparation method of a water-soluble carbon point modified perovskite type catalytic material, which comprises the following steps,
(1) mixing amino acid, alcohol and urea according to a proportion, wherein the urea can be replaced by citric acid, namely mixing the amino acid, the alcohol and the citric acid, and uniformly stirring until a transparent eutectic solvent DES is formed; the amino acid: alcohols: the molar ratio of urea or citric acid is 1: (4-6): (1-5); in the step (1), the amino acid is selected from one of glycine, lysine, arginine, cysteine, threonine, serine or histidine. In the step (1), the alcohol is selected from one of ethylene glycol, glycerol, polyethylene glycol 200, polyethylene glycol 400 or polyethylene glycol 800.
In the embodiment, urea is selected as a raw material, and the amino acid is arginine, specifically L-arginine; the alcohols are glycerol, amino acids: alcohols: the molar ratio of urea or citric acid is 1: 6: 3.
(2) weighing a perovskite metal precursor, a fuel and a fuel additive, wherein the perovskite metal precursor is two or more of rare earth metal nitrate, transition metal nitrate and alkaline earth metal nitrate; the fuel is one of urea, glycine, sucrose or citric acid; the fuel additive is one of ammonium acetate, starch or polyethylene glycol;
dissolving a perovskite metal precursor in deionized water, controlling the molar concentration of total metal ions in the solution to be 0.5-2.0 mol/L, and then adding fuel and a fuel additive; the sum of the fuel and the fuel additive is 1 to 2 times of the sum of the total metal ions added before; the molar ratio of the fuel to the fuel additive is (2-5): 1; stirring for 0.5h at room temperature to obtain a precursor mixed solution, and roasting the precursor mixed solution for 3-6h at 650-850 ℃ to obtain a perovskite metal oxide catalyst;
preferably, the obtained precursor mixed solution is transferred to an evaporation dish and placed in an electric furnace for presintering to obtain loose powder, and then roasting is carried out.
In the embodiment, the perovskite metal precursor is rare earth metal nitrate and transition metal nitric acid, and the rare earth metal nitrate and the transition metal nitric acid are respectively selected from nitrate of La and nitrate of Co; the fuel is urea; the fuel additive is ammonium acetate; the total metal ion molar concentration in the solution is 1 mol/L; the molar number of the sum of the fuel and the fuel additive is 1.5 times of the molar number of the sum of all the added metal ions; the molar ratio of fuel to fuel additive is 4: 1; roasting the precursor mixed solution at 700 ℃ for 3h to obtain a perovskite metal oxide catalyst;
(3) mixing the transparent eutectic solvent obtained in the step (1) and the perovskite obtained in the step (2)
Mixing the ore metal oxide catalyst with deionized water, and adding the deionized water according to the proportion of 2-10mL of deionized water added into the perovskite metal oxide catalyst obtained in the step (2) per gram; the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1 (1-6);
in this example, the amount of deionized water added was added in accordance with the ratio of 2mL of deionized water per gram of perovskite metal oxide catalyst; the mass ratio of the eutectic solvent to the perovskite metal oxide catalyst is 1: 2.
(4) Putting the product obtained in the step (3) into a reaction kettle, sealing and reacting for 3-7h at the temperature of 180-; in the embodiment, in the step (4), the reaction temperature is 200 ℃ and the reaction time is 4 hours;
(5) naturally cooling, alternately washing with ethanol and deionized water, and filtering for 5 times;
(6) and (4) drying the product obtained in the step (5) at 80 ℃, and then roasting for 1-3h at 600 ℃.
In the embodiment, in the step (6), the product is dried at 80 ℃, heated to 600 ℃ at 3 ℃/min, and then roasted at 600 ℃ for 1 h. The water-soluble carbon dot modified perovskite-type catalytic material LaCoO of example 1 was obtained3。
Evaluation of perovskite-type catalytic Material LaCoO modified with aqueous solution of carbon Point formed by Using L-arginine and Glycerol as carbon precursors in example 1 with a catalytic evaluation apparatus3The prepared catalyst of example 1 was used in an amount of 1mL, carrier gas flow rate of 100 mL/min, and methane concentration of 10000 ppm. The picture of the activity test of the final product of this example 1 is shown in FIG. 1, from which it can be seen that T is50%=396 ℃, which shows that the perovskite type catalytic material LaCoO modified by carbon dots in example 1 of the invention3The catalytic degradation of methane has obvious advantages. The XRD pattern of the final product of this example 1 is shown in FIG. 3, from which it can be seen that the perovskite type catalytic material LaCoO modified by carbon dots of this example3Carbon species are formed on the surface. The FT-IR spectrum of the final product of example 1 is shown in FIG. 5, and it can be seen that the perovskite-type catalytic material modified by the carbon points of example 1 has the following: C-OH stretching vibration (3209--1），C-H（2921 cm-1），C=ONR（1664 cm-1) Surface hydroxyl and amide, etc. water soluble groups, and the proper chemically reactive groups are favorable for adsorbing and cracking methane molecules, so that the methane is catalyzed and degraded more efficiently.
Example 2
The embodiment provides a preparation method of a water-soluble carbon point modified perovskite type catalytic material, which comprises the following steps,
(1) mixing amino acid, alcohol and urea according to a proportion, wherein the urea can be replaced by citric acid, namely mixing the amino acid, the alcohol and the citric acid, and uniformly stirring until a transparent eutectic solvent DES is formed; the amino acid: alcohols: the molar ratio of urea or citric acid is 1: (4-6): (1-5); in the step (1), the amino acid is selected from one of glycine, lysine, arginine, cysteine, threonine, serine or histidine. In the step (1), the alcohol is selected from one of ethylene glycol, glycerol, polyethylene glycol 200, polyethylene glycol 400 or polyethylene glycol 800.
In the embodiment, citric acid is selected as a raw material, and amino acid is lysine; the alcohol is glycol, amino acid: alcohols: the molar ratio of urea or citric acid is 1: 5: 2.5.
(2) weighing a perovskite metal precursor, a fuel and a fuel additive, wherein the perovskite metal precursor is two or more of rare earth metal nitrate, transition metal nitrate and alkaline earth metal nitrate; the fuel is one of urea, glycine, sucrose or citric acid; the fuel additive is one of ammonium acetate, starch or polyethylene glycol;
dissolving a perovskite metal precursor in deionized water, controlling the molar concentration of total metal ions in the solution to be 0.5-2.0 mol/L, and then adding fuel and a fuel additive; the sum of the fuel and the fuel additive is 1 to 2 times of the sum of the total metal ions added before; the molar ratio of the fuel to the fuel additive is (2-5): 1; stirring for 0.5h at room temperature to obtain a precursor mixed solution, and roasting the precursor mixed solution for 3-6h at 650-850 ℃ to obtain a perovskite metal oxide catalyst; preferably, the obtained precursor mixed solution is transferred to an evaporation dish and placed in an electric furnace for presintering to obtain loose powder, and then roasting is carried out.
In the embodiment, the perovskite metal precursor is rare earth metal nitrate, transition metal nitrate and alkaline earth metal nitrate, and the rare earth metal nitrate, the transition metal nitrate and the alkaline earth metal nitrate are respectively selected from nitrate of La, nitrate of Mn and nitrate of Mg; the fuel is glycine; the fuel additive is ammonium acetate; the total metal ion molar concentration in the solution is 1.2 mol/L; the molar number of the sum of the fuel and the fuel additive is 2 times of the sum of the molar numbers of all the added metal ions; the molar ratio of fuel to fuel additive is 5: 1; roasting the precursor mixed solution at 800 ℃ for 5 hours to obtain a perovskite metal oxide catalyst;
(3) mixing the transparent eutectic solvent obtained in the step (1) and the perovskite obtained in the step (2)
Mixing the ore metal oxide catalyst with deionized water, and adding the deionized water according to the proportion of 2-10mL of deionized water added into the perovskite metal oxide catalyst obtained in the step (2) per gram; the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1 (1-6);
in this example, the amount of deionized water added was added in accordance with the ratio of 7mL of deionized water per gram of perovskite metal oxide catalyst; the mass ratio of the eutectic solvent to the perovskite metal oxide catalyst is 1: 3.
(4) Putting the product obtained in the step (3) into a reaction kettle, sealing and reacting for 3-7h at the temperature of 180-; in the embodiment, in the step (4), the reaction temperature is 230 ℃ and the reaction time is 6 hours;
(5) naturally cooling, alternately washing and filtering with ethanol and deionized water for 6 times;
(6) and (4) drying the product obtained in the step (5) at 80 ℃, and then roasting for 1-3h at 600 ℃.
In the embodiment, in the step (6), the product is dried at 80 ℃, heated to 600 ℃ at 3 ℃/min, and then roasted at 600 ℃ for 3 h. The water-soluble carbon dot modified perovskite type catalytic material LaMn of example 2 is obtained0.9Mg0.1O3。
By means of catalytic evaluation devicesEvaluation of the perovskite-type catalytic Material LaMn modified with an aqueous solution of carbon points formed by lysine and ethylene glycol as carbon precursors in example 20.9Mg0.1O3The prepared catalyst of example 2 was taken as 1mL, the carrier gas flow rate was 100 mL/min, and the methane concentration was 10000 ppm. The activity test picture of the final product obtained in this example 2 is shown in FIG. 2, from which it can be seen that T is50%=421 ℃, which shows that the perovskite catalytic material modified by the water-soluble carbon dots of example 2 of the present invention has a significant advantage in catalytic degradation of methane.
The XRD pattern of the final product of example 2 is shown in FIG. 4, from which it can be seen that carbon substances are formed on the surface of the perovskite-type catalytic material modified by the water-soluble carbon dots of this example. The FT-IR spectrum of the final product of example 2 is shown in FIG. 6, and it can be seen that the perovskite-type catalytic material modified by the water-soluble carbon dots of the example has the following: C-OH stretching vibration (3209--1），C-H（2921 cm-1），C=ONR（1664 cm-1) Surface hydroxyl and amide, etc. water soluble groups, and the proper chemically reactive groups are favorable for adsorbing and cracking methane molecules, so that the methane is catalyzed and degraded more efficiently.
Example 3
The embodiment provides a preparation method of a water-soluble carbon point modified perovskite type catalytic material, which comprises the following steps,
(1) mixing amino acid, alcohol and urea according to a proportion, wherein the urea can be replaced by citric acid, namely mixing the amino acid, the alcohol and the citric acid, and uniformly stirring until a transparent eutectic solvent DES is formed; the amino acid: alcohols: the molar ratio of urea or citric acid is 1: (4-6): (1-5); in the step (1), the amino acid is selected from one of glycine, lysine, arginine, cysteine, threonine, serine or histidine. In the step (1), the alcohol is selected from one of ethylene glycol, glycerol, polyethylene glycol 200, polyethylene glycol 400 or polyethylene glycol 800.
In the embodiment, urea is selected as a raw material, and the amino acid is threonine; the alcohol is polyethylene glycol 200, amino acid: alcohols: the molar ratio of urea or citric acid is 1: 4: 1.
(2) weighing a perovskite metal precursor, a fuel and a fuel additive, wherein the perovskite metal precursor is two or more of rare earth metal nitrate, transition metal nitrate and alkaline earth metal nitrate; the fuel is one of urea, glycine, sucrose or citric acid; the fuel additive is one of ammonium acetate, starch or polyethylene glycol;
dissolving a perovskite metal precursor in deionized water, controlling the molar concentration of total metal ions in the solution to be 0.5-2.0 mol/L, and then adding fuel and a fuel additive; the sum of the fuel and the fuel additive is 1 to 2 times of the sum of the total metal ions added before; the molar ratio of the fuel to the fuel additive is (2-5): 1; stirring for 0.5h at room temperature to obtain a precursor mixed solution, and roasting the precursor mixed solution for 3-6h at 650-850 ℃ to obtain a perovskite metal oxide catalyst;
preferably, the obtained precursor mixed solution is transferred to an evaporation dish and placed in an electric furnace for presintering to obtain loose powder, and then roasting is carried out.
In the embodiment, the perovskite metal precursor is alkaline earth metal nitrate and transition metal nitrate, and the alkaline earth metal nitrate and the transition metal nitrate are respectively selected from nitrate of Ca and nitrate of Fe; the fuel is sucrose; the fuel additive is starch; the total metal ion molar concentration in the solution is 0.5 mol/L; the molar number of the sum of the fuel and the fuel additive is 1 time of the sum of the molar numbers of all the added metal ions; the molar ratio of fuel to fuel additive is 2: 1; roasting the precursor mixed solution at 650 ℃ for 4h to obtain a perovskite metal oxide catalyst;
(3) mixing the transparent eutectic solvent obtained in the step (1) and the calcium obtained in the step (2)
Mixing the titanium ore metal oxide catalyst with deionized water, and adding the deionized water according to the proportion of 2-10mL of deionized water added into the perovskite metal oxide catalyst obtained in the step (2) per gram; the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1 (1-6);
in this example, the amount of deionized water added was added in accordance with the ratio of 10mL of deionized water per gram of perovskite metal oxide catalyst; the mass ratio of the eutectic solvent to the perovskite metal oxide catalyst is 1: 6.
(4) Putting the product obtained in the step (3) into a reaction kettle, sealing the reaction kettle and then performing temperature rise at 180℃ and 230 DEG C
Reacting for 3-7 h; in the embodiment, in the step (4), the reaction temperature is 210 ℃ and the reaction time is 7 hours;
(5) naturally cooling, alternately washing with ethanol and deionized water, and filtering for 4 times;
(6) and (4) drying the product obtained in the step (5) at 80 ℃, and then roasting for 2h at 600 ℃.
In the embodiment, in the step (6), the product is dried at 80 ℃, heated to 600 ℃ at 3 ℃/min, and then roasted at 600 ℃ for 3 h. The water-soluble carbon-point modified perovskite-type catalytic material CaFeO in example 3 was obtained3。
Evaluation of perovskite-type catalytic Material CaFeO modified with an aqueous solution of carbon points formed by threonine and polyethylene glycol 200 as carbon precursors in example 3 with a catalytic evaluation apparatus3The prepared catalyst of example 3 was taken as 1mL, the carrier gas flow rate was 100 mL/min, and the methane concentration was 10000 ppm. After testing, this example 3T50%=432 ℃, which shows that the perovskite-type catalytic material modified by carbon dots in example 3 of the present invention has a significant advantage in catalytic degradation of methane.
Example 4
The embodiment provides a preparation method of a water-soluble carbon point modified perovskite type catalytic material, which comprises the following steps,
(1) mixing amino acid, alcohol and urea according to a proportion, wherein the urea can be replaced by citric acid, namely mixing the amino acid, the alcohol and the citric acid, and uniformly stirring until a transparent eutectic solvent DES is formed; the amino acid: alcohols: the molar ratio of urea or citric acid is 1: (4-6): (1-5); in the step (1), the amino acid is selected from one of glycine, lysine, arginine, cysteine, threonine, serine or histidine. In the step (1), the alcohol is selected from one of ethylene glycol, glycerol, polyethylene glycol 200, polyethylene glycol 400 or polyethylene glycol 800.
In the embodiment, citric acid is selected as a raw material, and amino acid is cysteine; the alcohol is polyethylene glycol 400, amino acid: alcohols: the molar ratio of urea or citric acid is 1: 5: 5.
(2) weighing a perovskite metal precursor, a fuel and a fuel additive, wherein the perovskite metal precursor is two or more of rare earth metal nitrate, transition metal nitrate and alkaline earth metal nitrate; the fuel is one of urea, glycine, sucrose or citric acid; the fuel additive is one of ammonium acetate, starch or polyethylene glycol;
dissolving a perovskite metal precursor in deionized water, controlling the molar concentration of total metal ions in the solution to be 0.5-2.0 mol/L, and then adding fuel and a fuel additive; the sum of the fuel and the fuel additive is 1 to 2 times of the sum of the total metal ions added before; the molar ratio of the fuel to the fuel additive is (2-5): 1; stirring for 0.5h at room temperature to obtain a precursor mixed solution, and roasting the precursor mixed solution for 3-6h at 650-850 ℃ to obtain a perovskite metal oxide catalyst; preferably, the obtained precursor mixed solution is transferred to an evaporation dish and placed in an electric furnace for presintering to obtain loose powder, and then roasting is carried out.
In the embodiment, the perovskite metal precursor is rare earth nitrate, transition metal nitrate and alkaline earth metal nitrate, and the rare earth nitrate, the transition metal nitrate and the alkaline earth metal nitrate are respectively selected from nitrate of La, nitrate of Cr and nitrate of Sr; the fuel is citric acid; the fuel additive is polyethylene glycol; the total metal ion molar concentration in the solution is 2 mol/L; the molar number of the sum of the fuel and the fuel additive is 1.6 times of the molar number of the sum of all the added metal ions; the molar ratio of fuel to fuel additive was 3.8: 1; roasting the precursor mixed solution at 850 ℃ for 65 hours to obtain a perovskite metal oxide catalyst;
(3) mixing the transparent eutectic solvent obtained in the step (1) and the perovskite obtained in the step (2)
Mixing the ore metal oxide catalyst with deionized water, and adding the deionized water according to the proportion of 2-10mL of deionized water added into the perovskite metal oxide catalyst obtained in the step (2) per gram; the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1 (1-6);
in this example, the amount of deionized water added was added in accordance with the ratio of 3mL of deionized water per gram of perovskite metal oxide catalyst; the mass ratio of the eutectic solvent to the perovskite metal oxide catalyst is 1: 1.
(4) Putting the product obtained in the step (3) into a reaction kettle, sealing and reacting for 3-7h at the temperature of 180-; in the embodiment, in the step (4), the reaction temperature is 180 ℃ and the reaction time is 3 hours;
(5) naturally cooling, alternately washing with ethanol and deionized water, and filtering for 3 times;
(6) and (4) drying the product obtained in the step (5) at 80 ℃, and then roasting for 1-3h at 600 ℃.
In the embodiment, in the step (6), the product is dried at 80 ℃, heated to 600 ℃ at 3 ℃/min, and then roasted at 600 ℃ for 1.5 h. The water-soluble carbon dot-modified perovskite-type catalytic material La of example 4 was obtained0.9Sr0.1CrO3。
Evaluation of perovskite-type catalytic Material La modified with aqueous solution of carbon dots formed with cysteine and polyethylene glycol 400 as carbon precursors in example 4 by means of a catalytic evaluation apparatus0.9Sr0.1CrO3The prepared catalyst of example 4 was taken as 1mL, the carrier gas flow rate was 100 mL/min, and the methane concentration was 10000 ppm. After testing, T of example 450%And the temperature is =445 ℃, which shows that the perovskite catalytic material modified by the water-soluble carbon dots has obvious advantages in the catalytic degradation of methane in the embodiment 4 of the invention.
Example 5
The embodiment is different from the embodiment 1 in that a eutectic solvent DES is not added as a carbon precursor; the remaining steps and parameters were the same as in example 1. That is, in this example, in the step (3), the eutectic solvent is not added, and "mixing the transparent eutectic solvent obtained in the step (1) and the perovskite metal oxide catalyst obtained in the step (2) with deionized water" is changed to "mixing the perovskite metal oxide catalyst obtained in the step (2) with deionized water".
Example 6
The embodiment is different from the embodiment 2 in that a eutectic solvent DES is not added as a carbon precursor; the remaining steps and parameters were the same as in example 2. That is, in this example, in the step (3), the eutectic solvent is not added, and "mixing the transparent eutectic solvent obtained in the step (1) and the perovskite metal oxide catalyst obtained in the step (2) with deionized water" is changed to "mixing the perovskite metal oxide catalyst obtained in the step (2) with deionized water".
Final products obtained in examples 1-2 and examples 5-6 and LaCoO3As received and LaMn0.9Mg0.1O3Specific surface area and activity tests were performed as such and the test results are shown in table 1.
Table 1 results of activity test
As can be seen from table 1 and fig. 1 to 6, (1) examples 1 to 2 are superior to respective corresponding examples 5 to 6, compared to examples 5 to 6, and a hydrothermal method is also employed, except that the examples 5 to 6 do not add the eutectic solvent DES, that is, amino acid and alcohol are not added as carbon precursors; 3-4 XRD patterns can show that carbon substances are formed on the surface of the perovskite material in the examples 1-2; surface functional group characterization of the synthesized carbon-point modified perovskite material from the FT-IR plots of fig. 5-6 clearly reveals the following for examples 1-2 as compared to examples 5-6: C-OH stretching vibration (3209--1），C-H（2921 cm-1），C=ONR（1664 cm-1) Surface hydroxyl groups and water-soluble groups such as amide, which are suitable chemically reactive groups for adsorbing and cracking methane molecules and thus catalytically degrading methane more efficiently, examples 1-2 are superior to examples 5-6. The hydrothermal method of the preparation method avoids hard particle agglomeration possibly formed at high temperature; the obtained powder has good dispersibility, no agglomeration, good crystal form and controllable shape, and can be used for improving the defects (low specific surface area) of the materials prepared by the traditional sol-gel method;
the dissolution and recrystallization of elementary solid particles can be promoted in the secondary crystallization process, and when the particle size is larger than the critical size, the particle can continue to grow as a crystal nucleus and has an inhibiting effect on the subsequent growth; meanwhile, the carbon substance can cause the crystal structure of the perovskite metal oxide to change, more oxygen vacancies are generated, more active sites are exposed, and therefore methane can be degraded more efficiently.
(2) Examples 5 to 6 and LaCoO, respectively3As received and LaMn0.9Mg0.1O3Compared with the original samples, the products of examples 5 to 6 are respectively superior to the original samples, and both products are not added with carbon precursors, but are different in preparation method, so that the hydrothermal method disclosed by the invention is used for reducing the agglomeration phenomenon of catalyst particles, increasing the specific surface area and obviously enhancing the exposure of active sites, thereby more efficiently catalyzing and degrading methane. This shows that the preparation method of the invention avoids the hard agglomeration of particles which can be formed at high temperature; the obtained powder has good dispersibility, no agglomeration, good crystal form and controllable shape, and can be used for overcoming the defects (low specific surface area) of the traditional sol-gel method for preparing materials.
The specific surface area of the perovskite type catalytic material modified by the carbon points reaches 20-25m2The surface is added with a large number of water-soluble groups such as hydroxyl, amide and the like, and carbonaceous substances are formed on the surface, so that the catalytic activity is obviously improved. Such as a traditional sol-gel process prepared perovskite metal oxide catalyst LaCoO3 T50%=492 ℃, the activity is obviously improved after the hydrothermal modification by carbon points, T50%The value is reduced by about 100 ℃ at most. The optimized treatment method of the catalyst can be applied to the preparation of various metal oxide materials, such as hexachlorophosphate metal oxideCompound catalysts, spinel metal oxide catalysts, and the like. The perovskite metal oxide subjected to metal ion and hydrothermal optimization treatment can improve catalytic activity, reduce energy consumption, reduce emission of industrial waste gas, automobile exhaust and the like, and bring great economic and social benefits.
In this study we used a solution combustion method to prepare the perovskite catalytic material. The method can quickly form a metastable state phase, and the mixing of initial reactants occurs in a liquid state in the reaction process, so that the uniformity and the stoichiometry of a reaction product are conveniently controlled; the process is quick and does not need special equipment.
CDs synthesized by using molecules such as citrate, carbohydrate, polymer-silicon dioxide nano composite materials and the like as carbon precursors are usually quasi-spherical nano particles through hydrothermal or microwave synthesis and other 'bottom-up' methods, and have uniform dispersion, no apparent agglomeration and particle diameter of 2-6 nm. The oxidized CDs have the oxygen content ranging from 5 to 50 percent, contain a large number of water-soluble groups such as carboxyl, hydroxyl and amide on the surface, have excellent water solubility and appropriate chemically reactive groups, and are used for further physical and chemical property modification of materials. The amino acid DES selected by the method is a low-toxicity green solvent, has good thermal and chemical stability and has no biological toxicity. The amino acid molecule contains two functional groups of amino and carboxyl, and part of the amino acid has hydrophilicity. The carbon points formed by the amino acid DES as a carbon precursor are bonded to the surface of the perovskite catalyst in a free form or a bond, and the conjugated structure of the carbon points can promote the adsorption of methane to the surface of the perovskite, so that the carbon points are activated by hydroxyl and oxygen-free groups. At the same time, strong interactions between the perovskite metal oxide and the CDs exist to stabilize the complex and facilitate the charge transfer process, resulting in enhanced catalytic performance. In the field of heterogeneous catalysis, the invention utilizes the advantage of CDs functionalization to modify the physicochemical property of the surface of the perovskite catalyst, thereby developing a perovskite type catalytic material capable of catalyzing and degrading organic waste gas more efficiently, and having important significance.
In conclusion, the invention optimizes and treats the physicochemical properties of the surface of the perovskite type catalytic material by adding the carbon-containing precursors, namely amino acid, alcohol and urea or citric acid, for example, water-soluble groups such as carboxyl, hydroxyl and amide on the surface of the perovskite type catalytic material are added, and the appropriate chemically reactive groups are favorable for adsorbing and cracking methane molecules, thereby more efficiently catalyzing and degrading methane. The preparation method provided by the invention is simple and efficient, and has important significance for preparing the catalyst.
Claims (10)
1. A preparation method of a water-soluble carbon point modified perovskite type catalytic material is characterized by comprising the following steps: which comprises the following steps of,
(1) mixing amino acid, alcohol and urea or citric acid according to a proportion, and uniformly stirring until a transparent eutectic solvent is formed; the amino acid: alcohols: the molar ratio of urea or citric acid is 1: (4-6): (1-5);
(2) weighing a perovskite metal precursor, a fuel and a fuel additive, wherein the perovskite metal precursor is more than two of rare earth metal nitrate, transition metal nitrate and alkaline earth metal nitrate; the fuel is one of urea, glycine, sucrose or citric acid; the fuel additive is one of ammonium acetate, starch or polyethylene glycol;
dissolving a perovskite metal precursor in deionized water, controlling the molar concentration of total metal ions in the solution to be 0.5-2.0 mol/L, and then adding fuel and a fuel additive; the sum of the fuel and the fuel additive is 1 to 2 times of the sum of the total metal ions added before; the molar ratio of the fuel to the fuel additive is (2-5): 1; stirring for 0.5h at room temperature to obtain a precursor mixed solution, and roasting the precursor mixed solution for 3-6h at 650-850 ℃ to obtain a perovskite metal oxide catalyst;
(3) mixing the transparent eutectic solvent obtained in the step (1) and the perovskite metal oxide catalyst obtained in the step (2) with deionized water, and adding the deionized water according to the proportion of 2-10mL of deionized water added in each gram of the perovskite metal oxide catalyst obtained in the step (2); the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1 (1-6);
(4) putting the product obtained in the step (3) into a reaction kettle, sealing and reacting for 3-7h at the temperature of 180-;
(5) naturally cooling, and alternately washing and filtering for 3-6 times by using ethanol and deionized water;
(6) and (4) drying the product obtained in the step (5) at 80 ℃, and then roasting for 1-3h at 600 ℃.
2. The method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (1), the amino acid is selected from one of glycine, lysine, arginine, cysteine, threonine, serine or histidine.
3. The method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (1), the alcohol is selected from one of ethylene glycol, glycerol, polyethylene glycol 200, polyethylene glycol 400 or polyethylene glycol 800.
4. The method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in step (1), the amino acid: alcohols: the molar ratio of urea or citric acid is 1: 6: 3.
5. the method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (2), the method is characterized in that: the total metal ion molar concentration is 1 mol/L.
6. The method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (2), the method is characterized in that: the molar amount of the sum of the fuel and the fuel additive is 1.5 times the molar amount of the sum of all the metal ions added.
7. The method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (2), the method is characterized in that: the molar ratio of the fuel to the fuel additive is 4: 1.
8. the method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (3), the mass ratio of the transparent eutectic solvent obtained in the step (1) to the perovskite metal oxide catalyst obtained in the step (2) is 1: 2.
9. The method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (4), the reaction temperature is 200 ℃ and the reaction time is 4 h.
10. The method for preparing a water-soluble carbon dot modified perovskite-type catalytic material as claimed in claim 1, wherein: in the step (6), the product is dried at 80 ℃, heated to 600 ℃ at 3 ℃/min and then roasted at 600 ℃ for 1 h.
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