A Cu1 / CeO2 single-atom catalyst and its preparation method
By treating the CeO2 surface with ascorbic acid reducing agent, Cu1/CeO2 single-atom catalysts were prepared, which solved the problems of complex construction and poor dispersion of single-atom sites on the CeO2 surface, achieved high efficiency of catalytic activity and selectivity, and simplified the preparation process.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PEKING UNIV
- Filing Date
- 2024-01-30
- Publication Date
- 2026-05-26
AI Technical Summary
Existing methods for constructing single-atom sites on CeO2 surfaces are complex and have poor single-atom dispersion, which hinders the practical application of single-atom catalysts.
A Cu1/CeO2 single-atom catalyst was prepared by treating CeO2 support with ascorbic acid reducing agent and capturing Cu2+ atoms by injecting electrons into the CeO2 surface to prevent their migration and aggregation.
The prepared Cu1/CeO2 catalyst exhibits excellent catalytic activity and N2 selectivity, which are far superior to traditional doped catalysts and pure CeO2 catalysts. The synthesis route is simple and can be used for other single-atom metal oxide catalysts.
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Figure CN117884136B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of single-atom catalyst technology, and in particular to a Cu1 / CeO2 single-atom catalyst and its preparation method. Background Technology
[0002] As the size of nanoparticles decreases, the number of exposed surface atoms increases, and the atomic structure, electronic structure, and surface defects are all improved. Therefore, controlling the particle size to the atomic level to obtain single-atom catalysts is a method to maximize atom utilization efficiency and improve catalytic activity.
[0003] In the controllable synthesis of single-atom catalysts, the earliest proposed methods include traditional precipitation deposition and impregnation methods. In recent years, new synthetic strategies have been proposed, including thermal decomposition methods, electrochemical deposition methods, and atomic layer deposition (ALD) methods using metal-organic frameworks (MOFS) as templates. For example, patent CN114293223A discloses a method for preparing ultrafine cerium dioxide-supported metal single-atom catalysts from cluster-based framework materials. First, a cerium-oxygen cluster MOFS is prepared by mixing a metal salt solution of cerium ammonium nitrate and the organic ligand trimesic acid, and heating the mixture hydrothermally for 15–30 min. Then, the metal salt solution is immersed in the cerium-oxygen cluster MOFS for 12–24 h using an impregnation method, followed by washing and vacuum drying for 1–2 days to obtain a cluster-based chelated metal ion material. Finally, the cerium dioxide-supported metal single-atom catalyst M@CeO2@C is obtained by high-temperature carbonization under an inert atmosphere.
[0004] Despite the significant progress made by the aforementioned methods in this field, the preparation of single-atom catalysts remains complex, and their tendency to aggregate at high temperatures hinders their practical application. This is particularly true for the construction of single-atom sites on the CeO2 surface, where either the prepared samples exhibit poor single-atom dispersion or the preparation process is overly complex. Therefore, developing new methods for preparing CeO2-based single-atom catalysts remains crucial. Summary of the Invention
[0005] The purpose of this invention is to provide a Cu1 / CeO2 single-atom catalyst and its preparation method, so as to solve the problems of complex construction methods of single-atom sites on CeO2 surface and poor single-atom dispersion during preparation.
[0006] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a Cu1 / CeO2 single-atom catalyst, comprising the following steps:
[0007] (1) Disperse CeO2 in distilled water, add ascorbic acid, stir at room temperature, centrifuge, wash, and dry to obtain solid CeO2-R;
[0008] (2) Disperse CeO2-R in distilled water, add copper nitrate to adjust the solution to alkaline, stir, centrifuge, wash, and dry to obtain solid Cu1 / CeO2-W;
[0009] (3) Cu1 / CeO2-W was calcined under a protective atmosphere to obtain the product Cu1 / CeO2-R.
[0010] Preferably, the mass ratio of CeO2 to ascorbic acid in step (1) is 1:2.
[0011] Preferably, in step (2), the mass ratio of CeO2-R to copper nitrate is 4:1.
[0012] Preferably, in step (2), sodium carbonate solution is used to adjust the solution to be alkaline.
[0013] Preferably, in step (2), sodium carbonate solution is used to adjust the pH of the solution to >8.
[0014] Preferably, in step (3), the calcination is carried out at 300°C for 2 hours, and the protective atmosphere is one or both of hydrogen and nitrogen.
[0015] Preferably, in step (1), the mixture is stirred at room temperature for 6 hours, and in step (2), it is stirred for 12 hours.
[0016] Preferably, in both steps (1) and (2), the washing is performed 4 times with distilled water.
[0017] Preferably, the drying temperature in steps (1) and (2) is 80°C.
[0018] A second aspect of the present invention provides a Cu1 / CeO2 single-atom catalyst obtained by the preparation method described above.
[0019] The third aspect of the present invention provides an application of a Cu1 / CeO2 single-atom catalyst, which is used as a denitrification catalyst.
[0020] Therefore, the Cu1 / CeO2 single-atom catalyst with the above-described structure and its preparation method have the following beneficial effects:
[0021] (1) Electrons are injected into the surface of the flower-like CeO2 support through the adsorption of the reducing agent ascorbic acid (AA) (generating a large amount of Ce). 3 + These electrons can capture Cu through the attraction between positive and negative charges (sites). 2+ Atoms prevent copper ions from migrating and accumulating.
[0022] (2) By using this surface electron-rich CeO2 support to load Cu single atoms to maintain the stability of Cu single atom structure, the prepared Cu1 / CeO2 catalyst exhibits excellent catalytic activity and N2 selectivity, which is far superior to traditional doped catalysts and pure CeO2 catalysts.
[0023] (3) The synthesis route is simple and universal, and can be applied to the manufacture of other single-atom metal oxide catalysts.
[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description
[0025] Figure 1 This is a synthetic route diagram for CeO2 catalyst;
[0026] Figure 2 This is the synthetic route diagram for the Cu1 / CeO2-R catalyst;
[0027] Figure 3 These are XRD patterns of CeO2, CeO2-R, Cu1 / CeO2-R, Cu1 / CeO2-D, and Cu-doped CeO2 catalysts;
[0028] Figure 4 yes Figure 3 Rietveld's retouched photos;
[0029] Figure 5 These are SEM and TEM images of the CeO2 catalyst;
[0030] Figure 6 These are the N2 adsorption / desorption isotherms and pore size distribution diagrams for the CeO2 catalyst;
[0031] Figure 7 This is a TEM image of the Cu1 / CeO2-R catalyst;
[0032] Figure 8 This is the EDS elemental distribution diagram of the Cu1 / CeO2-R catalyst;
[0033] Figure 9 The graph shows the catalytic performance of Cu1 / CeO2-R, CeO2, CeO2-R, Cu1 / CeO2-D, and Cu-doped CeO2 catalysts. Detailed Implementation
[0034] The present invention will be further described below. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the present invention is not limited to this embodiment.
[0035] Example 1
[0036] like Figure 1 As shown, the preparation method of CeO2 support is as follows:
[0037] Place 160 ml of deionized water into a 200 ml beaker. Dissolve 0.02 mol of glucose in the water and stir magnetically for 30 minutes. Then, add 0.03 mol of acrylamide and 0.01 mol of cerium nitrate hexahydrate to the glucose solution sequentially, and continue stirring for at least 2 hours. After thorough stirring, add 12 mL of ammonia solution dropwise to the resulting solution to adjust the pH to no lower than 10. During this process, the solution will darken in color. Continue stirring at room temperature for 5 hours to form a homogeneous gel.
[0038] After stirring, the mixture was transferred to a 200 mL hydrothermal reactor (filling degree not exceeding 80%) and placed in an oven at 180 °C for 72 h. The solid product was then obtained by filtration or centrifugation and washed with water and ethanol alternately at least 6 times. The precipitate after washing was dried in a vacuum oven at 70 °C for 24 h.
[0039] Subsequently, the product was calcined in a tube furnace at 600°C for 6 hours in a N2 atmosphere (heating rate 5°C / min), and then calcined in a muffle furnace at 400°C for 4 hours to obtain flower-shaped CeO2.
[0040] like Figure 2 As shown, the preparation steps of the Cu1 / CeO2-R catalyst are as follows:
[0041] The CeO2 (100 mg) was dispersed in distilled water (200 mL), and ascorbic acid (200 mg) was added. The mixture was then stirred vigorously at room temperature for 6 h. The solid particles were collected by centrifugation, washed four times with distilled water (30 mL), and dried overnight at 80 °C. The product obtained in this step is designated CeO2-R.
[0042] 400 mg CeO2-R was redispersed in distilled water (80 mL), and 100 mg copper nitrate (Cu(NO3)2·3H2O) was added. The solution was adjusted to alkalinity using sodium carbonate (Na2CO3) solution. After stirring for 12 hours, the product was collected by centrifugation, washed four times with distilled water, and then dried in a vacuum drying oven at 80 °C for 24 hours. The product obtained in this step is designated as Cu1 / CeO2-W.
[0043] Next, Cu1 / CeO2-W was calcined at 300℃ in an H2 / N2 atmosphere for 2 hours, and the final product was indicated as Cu1 / CeO2-R.
[0044] Comparative Example 1
[0045] The difference from Example 1 is that ascorbic acid was not added, and the resulting product is represented as Cu1 / CeO2-D.
[0046] Comparative Example 2
[0047] The preparation process of the Cu-doped CeO2 catalyst is as follows:
[0048] 160 ml of deionized water was placed in a 200 ml beaker. Glucose (0.02 mol) was dissolved in the water and magnetically stirred for 30 minutes. Then, acrylamide (0.03 mol), cerium nitrate hexahydrate (0.01 mol), and copper nitrate trihydrate (0.001 mol) were added to the glucose solution sequentially, and the mixture was stirred continuously for 2 hours. After thorough stirring, 12 mL of ammonia solution was added dropwise to the resulting solution to adjust the pH to not be lower than 10. During this process, the color of the solution deepened. The mixture was stirred continuously at room temperature for 5 hours to form a homogeneous gel.
[0049] After stirring, the mixture was transferred to a 200 mL hydrothermal reactor (filling degree not exceeding 80%) and placed in an oven at 180 °C for 72 h. The solid product was then obtained by filtration or centrifugation and washed with water and ethanol alternately at least 6 times. The precipitate after washing was dried in a vacuum oven at 70 °C for 24 h.
[0050] Subsequently, the product was calcined in a tube furnace at 600°C for 6 hours in a N2 atmosphere (heating rate 5°C / min), and then calcined in a muffle furnace at 400°C for 4 hours to finally obtain flower-shaped Cu-doped CeO2.
[0051] Experimental Example 1
[0052] (1) XRD tests were performed on the CeO2, CeO2-R, Cu1 / CeO2-R, Cu1 / CeO2-D and Cu-doped CeO2 catalysts in Example 1.
[0053] from Figure 3-4 The XRD patterns of each catalyst can be seen in the image. The synthesized CeO2 nanoflower support is a cubic fluorite phase CeO2 (JCPDS NO.34-0394). The Cu1 / CeO2-R catalyst maintains the cubic fluorite phase of the CeO2 catalyst, indicating that the loading of copper atoms has no effect on the crystal phase of CeO2 itself.
[0054] To investigate whether Cu-related phases formed, the XRD patterns of the CeO2 support, CeO2-R, and Cu1 / CeO2-R catalysts were first refined using Rietveld, such as... Figure 4As shown in the figure, the XRD pattern of Cu1 / CeO2-R only shows diffraction peaks of cubic fluorite CeO2, and no other diffraction peaks were found, indicating that no Cu-related nanoparticles were formed. Table 1 shows the grain size, cell parameters, and microstructure parameters of each catalyst. No severe lattice distortion was found in the Cu1 / CeO2-R catalyst, which rules out the possibility of forming Cu-Ce solid solution and Cu-doped CeO2.
[0055] Table 1. Rietveld refined structural parameters of the catalyst
[0056]
[0057] (2) The CeO2 catalyst in Example 1 was subjected to SEM, TEM and specific surface area tests.
[0058] Figure 5 The morphology and crystal plane information of the prepared CeO2 are shown. Figure 5 (a) and Figure 5 (b) The synthesized CeO2 is shown to be in the form of nanoflowers. Figure 5 (c) The HR-TEM image shows clear lattice fringes with a lattice spacing of This corresponds to the (111) plane of CeO2. This indicates that the CeO2 catalyst was successfully synthesized.
[0059] Figure 6 The N2 adsorption / desorption isotherms and pore size distribution of the CeO2 catalyst are shown, with a specific surface area of 260 m². 2 / g, with a pore size distribution of approximately 3.7646 nm. The nanoflower morphology has a large surface area, and as a carrier, it can provide abundant adsorption sites for Cu single atoms, which helps to increase the number of single-atom sites. Using the above CeO2 nanoflowers as a carrier, it was ultrasonically dispersed in deionized water, and AA was added and stirred vigorously. During the experiment, it was observed that the color of CeO2 immediately changed from pale yellow-white to dark brown after being treated by AA molecules, indicating that the CeO2 surface was reduced.
[0060] This indicates that a large amount of Ce was generated in CeO2 nanoflowers due to ascorbic acid modification. 3+ Therefore, compared to the original CeO2, the CeO2-R support contains more CeO2. 3+ With more sites, the reducing power of the catalyst atoms anchored on the surface becomes stronger. According to ICP-AES analysis, the Cu loading in the Cu1 / CeO2-R catalyst is 3.25 wt%. In the absence of AA assistance, the amount of Cu supported on the original CeO2 support is lower (approximately 0.78 wt%) for the Cu1 / CeO2-D catalyst, which demonstrates that the surface reduction state of the CeO2 support helps to anchor Cu species on the support.
[0061] (3) The Cu1 / CeO2-R catalyst in Example 1 was subjected to TEM and EDS tests.
[0062] like Figure 7 As shown, the loading on the Cu1 / CeO2-R catalyst was determined by TEM. In bright-field TEM and high-resolution TEM images, Cu1 / CeO2-R appeared indistinguishable from the original flower-like CeO2, and no Cu-related nanoclusters or nanoparticles were observed. Combined with XRD characterization results, Cu1 / CeO2-R maintained the cubic fluorite cerium dioxide structure without the appearance of new peaks, indicating that Cu is highly dispersed on the CeO2 surface. Even higher-resolution HAADF-STEM images did not reveal Cu nanoclusters or particles. Figure 8 As shown, brighter spots appear randomly in the ordered atomic array. These brighter spots may be Cu atoms loaded on the surface. The EDS elemental distribution map confirms the uniform distribution of Cu and Ce elements.
[0063] Experimental Example 2
[0064] To evaluate the SCR catalytic performance of CeO2, CeO2-R, Cu1 / CeO2-R, Cu1 / CeO2-D, and Cu-doped CeO2 catalysts, the catalysts were subjected to 30,000 h⁻¹. -1 The SCR reaction performance was evaluated at a high space velocity (GHSV).
[0065] like Figure 9 As shown in (a) and (b), the NO conversion and N2 selectivity of the catalysts change with temperature, respectively. Under these conditions, the highest NO conversion rates for CeO2, Cu-doped CeO2, and Cu1 / CeO2-D are only ~65%, ~75%, and ~80%, respectively. However, after constructing Cu single-atom sites on the CeO2 surface, the NO conversion rate of the catalyst is significantly improved, and the Cu1 / CeO2-R catalyst exhibits the best NH3-SCR activity, with its NO conversion rate remaining above 95% in the temperature range of 150–270 °C. In addition, the Cu1 / CeO2-R catalyst also exhibits excellent N2 selectivity (>96%) over a wide temperature range.
[0066] like Figure 9As shown in (c) and (d), the reactivity of the catalyst to NO + O2 and to NH3 + O2 was also evaluated, and the catalyst performance was further investigated. The addition of a Cu single atom to CeO2 enhanced the catalytic activity for NH3 oxidation, and the ignition temperature of the NH3 oxidation reaction decreased from 300℃ (CeO2) to 120℃ (Cu1 / CeO2-R). This indicates that Cu1 / CeO2-R has a significantly better ability to activate NH3 than the CeO2 catalyst. Figure 9 As shown in (d), the ignition temperature of the NO oxidation reaction also decreased from 270℃ (CeO2) to 210℃ (Cu1 / CeO2-R), indicating that introducing Cu single-atom sites into CeO2 also greatly promoted the NO oxidation reaction. The ignition temperature of the NH3 oxidation reaction was basically consistent with that of the SCR reaction, suggesting that promoting NH3 adsorption and activation may be the main pathway by which Cu single-atom catalysts promote the SCR reaction.
[0067] Therefore, this invention employs a Cu1 / CeO2 single-atom catalyst with the above-described structure and its preparation method. Through the adsorption of the reducing agent ascorbic acid, electrons are injected into the surface of the flower-like CeO2 support. These electrons can capture Cu due to the attraction between positive and negative charges. 2+ The atom prevents copper ion migration and aggregation. The preparation method is simple. The prepared Cu1 / CeO2-R catalyst exhibits excellent denitration catalytic activity and N2 selectivity, which is far superior to traditional doped catalysts and pure CeO2 catalysts.
[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.
Claims
1. An application of a Cu1 / CeO2 single-atom catalyst, characterized in that: The Cu1 / CeO2 single-atom catalyst is applied to the NH3-SCR reaction; within the temperature range of 150-270℃, the Cu1 / CeO2 single-atom catalyst achieves a NO conversion rate of ≥95% and a N2 selectivity of >96%. The preparation method of the Cu1 / CeO2 single-atom catalyst includes the following steps: (1) Disperse the flower-like CeO2 in distilled water, add ascorbic acid, and generate Ce on the surface of CeO2. 3+ The site was stirred at room temperature, centrifuged, washed, and dried to obtain solid CeO2-R; The mass ratio of CeO2 to ascorbic acid is 1:
2. (2) Disperse CeO2-R in distilled water, add copper nitrate to adjust the solution to alkaline, stir, centrifuge, wash, and dry to obtain solid Cu1 / CeO2-W; The mass ratio of CeO2-R to copper nitrate is 4:
1. (3) Cu1 / CeO2-W was calcined under a protective atmosphere to obtain the product Cu1 / CeO2-R; The protective atmosphere is hydrogen and nitrogen.
2. The application of the Cu1 / CeO2 single-atom catalyst according to claim 1, characterized in that: In step (2), sodium carbonate solution is used to adjust the solution to be alkaline.
3. The application of the Cu1 / CeO2 single-atom catalyst according to claim 2, characterized in that: In step (3), the sample is calcined at 300°C for 2 hours.
4. The application of the Cu1 / CeO2 single-atom catalyst according to claim 3, characterized in that: In step (1), the mixture is stirred at room temperature for 6 hours, and in step (2), it is stirred for 12 hours.
5. The application of the Cu1 / CeO2 single-atom catalyst according to claim 4, characterized in that: In both steps (1) and (2), the product is washed four times with distilled water.
6. The application of the Cu1 / CeO2 single-atom catalyst according to claim 5, characterized in that: The drying temperature in steps (1) and (2) is 80°C.