Monatomic catalyst for denitration and sulfur resistance and preparation method thereof

Abstract

The preparation method comprises the following steps: coating a spherical inorganic substance serving as a carrier with 6-methyluracil, and in the process, carrying out polymerization reaction on the 6-methyluracil serving as a precursor of a carbon source and a nitrogen source to generate a nitrogen-doped carbon material; meanwhile, cerium single atoms are anchored on the catalyst, then unreacted spherical inorganic substances are removed through calcination and acid pickling, and the single atom catalyst is obtained. The three-dimensional porous monatomic carbon catalyst with various microenvironment structures and pore structures is controllably synthesized by using an in-situ polymerization method, and has efficient denitration and sulfur resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing functional shaped single-atom catalysts, and particularly relates to a single-atom catalyst for denitrification and sulfur resistance and a preparation method thereof. Background Art

[0002] Energy is the fundamental driving force for economic development but also the root cause of pollution. Environmental pollution includes air pollution, water environmental pollution, soil pollution, etc. Among them, air pollution has become a difficult problem that all countries in the world must face during the industrialization process. And air environmental pollution has caused varying degrees of harm to human health and various organisms, seriously affecting the physical and mental health and quality of life of humans and causing huge losses to society. Among them, NO x is one of the main pollutants of air environmental pollution. Therefore, researching and developing NO x treatment technology is still one of the main tasks of current air pollution prevention and control.

[0003] As is well known, the surface free energy and specific activity of nanomaterials will increase sharply with the decrease of particle size. Therefore, single-atom catalysts (SACs) have many unique advantages. For example, metal elements are dispersed on the substrate material at the atomic level, which can fully expose all active sites, thus facilitating the improvement of the catalyst activity and achieving the highest atomic utilization rate; single metal atoms with extremely high surface free energy and high activity may cause quantum size effects; in addition, the special interaction between metal atoms and the substrate may promote charge transfer or provide an unsaturated coordination environment for metal atoms, which is beneficial to improving catalytic activity and selectivity. Typical SACs are mainly dispersed on oxides, sulfides, carbon-based materials or metal supports. Nowadays, single-atom catalysts have become a research hotspot in various fields due to their unique advantages and have been widely applied to a series of redox reaction systems, such as CO oxidation, CO 2 reduction, oxygen reduction reaction (ORR), selective hydrogenation, photocatalyst, etc. However, there is currently no report on the successful application of single-atom catalysts in the field of denitrification and sulfur resistance. Summary of the Invention

[0004] The purpose of the present invention is to provide a single-atom catalyst for efficient denitrification and sulfur resistance and a preparation method thereof.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: A single-atom catalyst for denitrification and sulfur resistance, which uses spherical inorganic substances as the carrier, is coated with 6-methyluracil, and in this process, 6-methyluracil is used as the precursor of the carbon source and nitrogen source, and through a polymerization reaction, a nitrogen-doped carbon material is generated, and at the same time, cerium single atoms are anchored on it. After that, it is obtained by calcination and pickling to remove the unreacted spherical inorganic substances. The preparation method of the single-atom catalyst includes the following steps: (1) Add 6-methyluracil to deionized water and obtain a methyluracil solution through ultrasonic dispersion; (2) Dissolve cerium nitrate in deionized water and obtain a cerium nitrate solution through ultrasonic dispersion; (3) Add the cerium nitrate solution to the 6-methyluracil solution and add spherical inorganic substances for polymerization reaction; (4) After freeze-drying the product obtained in step (3), calcine it under a nitrogen atmosphere, and then perform pickling to obtain the single-atom catalyst CeN x O 4-x / G (where x represents an integer from 1 to 4).

[0006] Furthermore, the spherical inorganic substance includes any one of silicon dioxide, aluminum oxide, and zirconium oxide.

[0007] Furthermore, the concentration of the methyluracil solution obtained in step (1) is 20 mg / mL.

[0008] Furthermore, the concentration of the cerium nitrate solution obtained in step (2) is 2 mg / mL.

[0009] Furthermore, the ultrasonic dispersion time in steps (1) and (2) is 20 - 30 min.

[0010] Furthermore, the material dosage in step (3) is calculated according to the mass ratio of cerium nitrate, 6-methyluracil, and spherical inorganic substances in the reaction system being 1:10:10.

[0011] Furthermore, the temperature of the polymerization reaction in step (3) is 90 - 100 °C and the time is 2 hours.

[0012] Furthermore, the heating rate of the calcination in step (4) is 5 °C / minute, the temperature is 800 - 1200 °C, and the time is 3 - 4 hours.

[0013] The advantages of the present invention are as follows: (1) The present invention uses spherical inorganic substances as templates, enabling the synthesized single-atom catalyst to more effectively increase the specific surface area and reaction active sites, thereby making the catalyst more stable and efficient in denitrification and sulfur resistance, and being beneficial to increasing the service life of the catalyst.

[0014] (2) 6-Methyluracil used in the present invention is inexpensive and easily accessible. Moreover, it has a rich source of heteroatoms and can form various single-atom coordination forms, which is conducive to the improvement of catalytic activity. At the same time, 6-methyluracil has special -N-C=S and -N-C=O structures, which are rich in electron vacancies and are conducive to the design and construction of the coordination environment at close range and the electron interaction at long range of the single-atom carbon-based catalyst. It is a promising precursor material for single-atom carbon-based catalysts.

[0015] (3) The synthesis reaction of the present invention can be carried out in a low-temperature environment. The reaction operation is simple, the reaction is rapid, there is no specific requirement for the reaction vessel, and the synthesized substance is not polluting to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the EDX elemental scanning diagram of the single-atom catalyst prepared in Example 3.

[0017] Figure 2 It is the schematic structural diagram of the tubular SCR reactor for catalyst activity testing; in the figure, 1 is the gas source; 2 is the pressure reducing valve; 3 is the mass flowmeter; 4 is the mixer; 5 is the air preheater; 6 is the catalytic bed; 7 is the catalyst; 8 is the flue gas analyzer.

[0018] Figure 3 It is the diagram of the catalytic stability of the single-atom catalyst prepared in Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] A single-atom catalyst for denitrification and sulfur resistance, and its preparation method includes the following steps: (1) Add 6-methyluracil to deionized water and ultrasonically disperse it for 20 - 30 min to obtain a 6-methyluracil solution with a concentration of 20 mg / mL; (2) Dissolve cerium nitrate in deionized water and ultrasonically disperse it for 20 - 30 min to obtain a cerium nitrate solution with a concentration of 2 mg / mL; (3) According to the mass ratio of cerium nitrate, 6-methyluracil to spherical inorganic matter being 1:10:10, add the cerium nitrate solution to the 6-methyluracil solution and add spherical inorganic matter, and react in an oil bath at 90 - 100 °C for 2 hours; (4) After freeze-drying the product obtained in step (3) for 24 hours, heat it to 800 - 1200 °C at a rate of 5 °C per minute under a nitrogen atmosphere and calcine it for 3 - 4 hours, and then pickle it with a 25 vol% hydrofluoric acid solution for 40 minutes to obtain the single-atom catalyst CeN x O 4-x / G (where x represents an integer from 1 to 4).

[0020] Among them, the spherical inorganic substance includes any one of silicon dioxide, aluminum oxide, and zirconium oxide.

[0021] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0022] Example 1 Accurately weigh 0.2 g of 6-methyluracil and dissolve it in 10 mL of deionized water. Ultrasonically disperse for 20 min to prepare a methyluracil solution. Accurately weigh 0.02 g of cerium nitrate and dissolve it in 10 mL of deionized water. Ultrasonically disperse for 30 min to prepare a cerium nitrate solution. Add the prepared cerium nitrate solution to the methyluracil solution, and add 0.2 g of spherical silica. React in an oil bath at 95 °C for 2 hours, then place it in a freeze dryer for freeze-drying for 24 h. Then, heat it to 800 °C at a rate of 5 °C / min in a nitrogen atmosphere and calcine for 3 hours. After that, pickle it with a 25 vol% hydrofluoric acid solution for 40 minutes to obtain a CeO 4 / SiO 2 catalyst with a Ce loading of 20%.

[0023] Example 2 Accurately weigh 0.2 g of 6-methyluracil and dissolve it in 10 mL of deionized water. Ultrasonically disperse for 20 min to prepare a methyluracil solution. Accurately weigh 0.02 g of cerium nitrate and dissolve it in 10 mL of deionized water. Ultrasonically disperse for 30 min to prepare a cerium nitrate solution. Add the prepared cerium nitrate solution to the methyluracil solution, and add 0.2 g of spherical silica. React in an oil bath at 95 °C for 2 hours, then place it in a freeze dryer for freeze-drying for 24 h. Then, heat it to 900 °C at a rate of 5 °C / min in a nitrogen atmosphere and calcine for 3 hours. After that, pickle it with a 25 vol% hydrofluoric acid solution for 40 minutes to obtain a CeN 1 O 3 / SiO 2 catalyst with a Ce loading of 20%.

[0024] Example 3 Accurately weigh 0.2 g of 6-methyluracil and dissolve it in 10 mL of deionized water. Ultrasonically disperse it for 20 min to prepare a methyluracil solution. Accurately weigh 0.02 g of cerium nitrate and dissolve it in 10 mL of deionized water. Ultrasonically disperse it for 30 min to prepare a cerium nitrate solution. Add the prepared cerium nitrate solution to the methyluracil solution, and add 0.2 g of spherical silica. React in an oil bath at 95 °C for 2 hours, then place it in a freeze dryer for freeze-drying for 24 h. Then, under a nitrogen atmosphere, heat it to 1000 °C at a rate of 5 °C per minute and calcine for 3 hours. After that, pickle it with 25 vol% hydrofluoric acid solution for 40 minutes to obtain a CeN 2 O 2 / SiO 2 catalyst with a Ce loading of 20%.

[0025] Figure 1 Figure is the EDX elemental scanning map of the prepared single-atom catalyst. It can be seen from the figure that different elements (Ce, O, N, and C) can be evenly loaded on the surface of the catalyst, which also proves the successful loading of single-atom cerium on its surface.

[0026] Example 4 Accurately weigh 0.2 g of 6-methyluracil and dissolve it in 10 mL of deionized water. Ultrasonically disperse it for 20 min to prepare a methyluracil solution. Accurately weigh 0.02 g of cerium nitrate and dissolve it in 10 mL of deionized water. Ultrasonically disperse it for 30 min to prepare a cerium nitrate solution. Add the prepared cerium nitrate solution to the methyluracil solution, and add 0.2 g of spherical silica. React in an oil bath at 95 °C for 2 hours, then place it in a freeze dryer for freeze-drying for 24 h. Then, under a nitrogen atmosphere, heat it to 1100 °C at a rate of 5 °C per minute and calcine for 3 hours. After that, pickle it with 25 vol% hydrofluoric acid solution for 40 minutes to obtain a CeN 3 O / SiO 2 catalyst with a Ce loading of 20%.

[0027] Example 5 Accurately weigh 0.2 g of 6-methyluracil and dissolve it in 10 mL of deionized water. Ultrasonically disperse it for 20 min to prepare a methyluracil solution. Accurately weigh 0.02 g of cerium nitrate and dissolve it in 10 mL of deionized water. Ultrasonically disperse it for 30 min to prepare a cerium nitrate solution. Add the prepared cerium nitrate solution to the methyluracil solution, and add 0.2 g of spherical silica. React in an oil bath at 95 °C for 2 hours, then place it in a freeze dryer for freeze-drying for 24 h. Then, under a nitrogen atmosphere, heat it to 1200 °C at a rate of 5 °C per minute and calcine for 3 hours. After that, pickle it with 25 vol% hydrofluoric acid solution for 40 minutes to obtain a CeN 4 / SiO 2 catalyst with a Ce loading of 20%.

[0028] Comparative Example Accurately weigh 0.2 g of cerium nitrate and dissolve it in 10 mL of deionized water. Ultrasonically disperse for 30 min to prepare a cerium nitrate solution, and then drop it onto the surface of 0.2 g of spherical silica. Place the above sample in an oven and dry it at 60 °C overnight, then heat it to 1100 °C at a rate of 5 °C / min in a nitrogen atmosphere and calcine for 3 hours. After that, pickle it with 25 vol% hydrofluoric acid solution for 40 minutes to finally obtain a Ce / SiO catalyst with a Ce loading of 20%. 2 Catalyst.

[0029] Catalytic activity evaluation: The denitrification and sulfur resistance performance of the catalyst was evaluated in the tubular SCR reactor as shown below. Figure 2 The reactor was externally electrically heated, and a thermocouple was placed beside the catalyst bed of the reaction tube to measure the temperature. The flue gas composition was simulated with steel cylinders, and the flue gas included NO, O 2 , N 2 , NH 3 as the reducing gas. The volume fractions of NO and NH 3 were both 0.05%, the volume fraction of O 2 was 5%, and the rest was N 2 . The gas flow rate was 700 mL·min -1 , and the temperature was controlled between 120 - 200 °C. The gas flow rate and composition were adjusted and controlled by mass flow meters. Gas analysis was performed using a British KM940 flue gas analyzer. To ensure the stability and accuracy of the data, each working condition was stabilized for at least 30 min. The test results are shown in Table 1.

[0030] Table 1 Results of Catalyst Performance Determination

[0031] It can be seen from the data in Table 1 that as the temperature continuously increases, the denitrification and sulfur resistance performance of the catalyst shows a trend of first increasing and then decreasing. Among them, the single-atom catalyst calcined at 1000 °C has the best denitrification and sulfur resistance rate.

[0032] Figure 3 It is a graph showing the catalytic stability of the single-atom catalyst prepared in Example 3. It can be seen from the graph that the catalyst has good stability within 20 h, and the denitrification rate can be maintained at about 88%.

[0033] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A method for preparing a single-atom catalyst for denitration and sulfur resistance, characterized in that: A spherical inorganic material is used as a carrier and coated with 6-methyluracil. In the process, 6-methyluracil is used as a precursor of a carbon source and a nitrogen source to generate a nitrogen-doped carbon material through a polymerization reaction, and at the same time, a single cerium atom is anchored thereon. The unreacted spherical inorganic material is then removed through calcination and acid washing to obtain the single atom catalyst.

2. The method for preparing a single atom catalyst according to claim 1, characterized in that: It specifically includes the following steps: (1) Add 6-methyluracil to deionized water and obtain a methyluracil solution by ultrasonic dispersion; (2) dissolving cerium nitrate in deionized water and obtaining a cerium nitrate solution by ultrasonic dispersion; (3) adding the cerium nitrate solution to the 6-methyluracil solution and adding the spherical inorganic substance to carry out a polymerization reaction; (4) The product after the reaction in step (3) is freeze-dried, calcined under a nitrogen atmosphere, and then acid-washed to obtain the single atom catalyst.

3. The method for preparing a single atom catalyst according to claim 1 or 2, characterized in that: The spherical inorganic material includes any one of silicon dioxide, aluminum oxide and zirconium oxide.

4. The method for preparing a single atom catalyst according to claim 2, characterized in that: The concentration of the methyl uracil solution obtained in step (1) is 20 mg / mL.

5. The method for preparing a single atom catalyst according to claim 2, characterized in that: The concentration of the cerium nitrate solution obtained in step (2) is 2 mg / mL.

6. The method for preparing a single atom catalyst according to claim 2, characterized in that: The amount of materials used in step (3) is calculated based on the mass ratio of cerium nitrate, 6-methyluracil and spherical inorganic substance in the reaction system of 1:10:

10.

7. The method for preparing a single atom catalyst according to claim 2, characterized in that: The polymerization reaction in step (3) is carried out at a temperature of 90-100° C. and for a time of 2 hours.

8. The method for preparing a single atom catalyst according to claim 2, characterized in that: The calcination temperature in step (4) is 800-1200°C and the calcination time is 3-4 hours.

9. A single atom catalyst prepared by the method according to any one of claims 1 to 8.

10. Use of the single-atom catalyst as claimed in claim 9 in denitrification and sulfur resistance.

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