A method for synthesizing a solid-phase single-atom catalyst

Abstract

The application discloses a kind of synthesis methods of solid phase single-atom catalyst, it is related to catalyst synthesis technical field.The application is after mixing cerium nitrate and manganese nitrate, dissolved in ethanol aqueous solution, obtain solution A;Glycerol and citric acid monohydrate are mixed and dissolved in ethanol aqueous solution, obtain solution B;Solution A and solution B are mixed to form transparent sol;After drying, solid powder is obtained;Solid powder is ball milled and then reduced calcination treatment, then ball milled and then second reduction calcination treatment;Finally, high-temperature calcination and low-temperature calcination treatment are carried out, and solid phase single-atom catalyst is obtained.The solid phase single-atom catalyst prepared by the application has excellent catalytic activity and can improve the denitration efficiency.

Description

Technical Field

[0001] This invention belongs to the field of catalyst synthesis technology, specifically relating to a method for synthesizing a solid-phase single-atom catalyst. Background Technology

[0002] Single-atom catalysts are catalysts in which a metal is uniformly and singly supported on a carrier such as a metal, metal oxide, two-dimensional material, or molecular sieve, with the single atom serving as the catalytic active center for the reaction. Currently, single-atom catalysts are widely used in oxidation reactions, electrocatalysis, photoelectrocatalysis, and hydrogenation catalysis.

[0003] Current single-atom catalyst synthesis processes are complex, use expensive raw materials, and have limited synthesis routes. Furthermore, the low loading of active metals in single-atom catalysts results in low catalytic activity and a short lifespan. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for synthesizing solid-phase single-atom catalysts. This invention is achieved using the following technical solution:

[0005] A method for synthesizing a solid-phase single-atom catalyst, characterized by comprising the following steps:

[0006] S1. Mix 3g of cerium nitrate and 0.1g to 0.2g of manganese nitrate, then dissolve them in a mixed solution of ethanol and water to obtain solution A, which is ready for use.

[0007] S2. Mix 1g of glycerol and 2g of citric acid monohydrate and dissolve them in a mixed solution of ethanol and water to obtain solution B, which is then set aside.

[0008] S3. Mix the solution A and the solution B and stir to form a transparent sol;

[0009] S4. Dry the transparent sol at 150℃~180℃ for 6h~8h to obtain a solid powder;

[0010] S5. The solid powder is ball-milled and then calcined at 250℃-270℃ for 2h-3h in a reducing atmosphere;

[0011] S6. After cooling the calcined solid powder, it is ball-milled and then calcined again at 250℃~270℃ for 2h~3h in a reducing atmosphere.

[0012] S6. The solid powder after secondary calcination is calcined at 800℃~1000℃ in a nitrogen atmosphere for 4h~6h, and finally calcined in a muffle furnace at 290℃~310℃ for 3h~4h to obtain a solid-phase single-atom catalyst.

[0013] Preferably, the mass ratio of ethanol to water in steps S1 and S2 is 1:1 to 2:1.

[0014] Preferably, the ball milling time for steps S5 and S6 is 2h to 4h.

[0015] Preferably, the reducing atmosphere in steps S5 and S6 is hydrogen.

[0016] Preferably, the manganese loading in the solid-phase single-atom catalyst is 0.89 wt% to 2.48 wt%.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] This invention involves dissolving a mixture of cerium nitrate and manganese nitrate in an aqueous ethanol solution to obtain solution A; dissolving a mixture of glycerol and citric acid monohydrate in an aqueous ethanol solution to obtain solution B; mixing solutions A and B to form a transparent sol; drying to obtain a solid powder; ball milling followed by reduction calcination, and then ball milling followed by a second reduction calcination; finally, high-temperature calcination and low-temperature calcination to obtain a solid-phase single-atom catalyst. The solid-phase single-atom catalyst prepared by this invention exhibits excellent catalytic activity and can improve denitrification efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the synthesis route of the Mn1 / CeO2 catalyst of the present invention;

[0020] Figure 2 The XRD Rietveld refinement results are shown for the catalysts prepared in Examples 1, 2, and 2 of this invention.

[0021] Figure 3 For comparative example 1MnO x XRD Rietveld refinement results for / CeO2 catalyst;

[0022] Figure 4 The images show: (a) aberration-corrected high-angle dark-field scanning transmission electron microscopy (AC-STEM HAADF) images and corresponding EELS spectra (b)-(c) of the Mn1 / CeO2-2 catalyst in Example 2; (d) a low-magnification HAADF-STEM image of the Mn1 / CeO2-2 catalyst and corresponding elemental distribution images of Ce (e), O (f), and Mn (g);

[0023] Figure 5 X-ray fine structure characterization of Mn1 / CeO2-2 catalyst; where (a) is the near-edge X-ray absorption structure (XANES) diagram of Mn K-edge; and (b) is the extended X-ray absorption fine structure (EXAFS) diagram of Fourier transform.

[0024] Figure 6 The denitrification performance of the catalysts prepared in Examples 1-2 and Comparative Examples 1-2 is shown in (a) for NO conversion, (b) for N2 selectivity, (c) for NH3 oxidation performance, and (d) for NO oxidation performance. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments.

[0026] Example 1

[0027] A method for synthesizing a solid-phase single-atom catalyst (Mn1 / CeO2-1) includes the following steps:

[0028] S1. Mix 3g of cerium nitrate and 0.1g of manganese nitrate, and then dissolve them in a 50% aqueous ethanol solution (ethanol to water in a 1:1 mass ratio) to obtain solution A, which is ready for use.

[0029] S2. Mix 1g of glycerol and 2g of citric acid monohydrate and dissolve them in a 50% ethanol aqueous solution (ethanol to water mass ratio of 1:1) to obtain solution B, which is then set aside.

[0030] S3. Mix the solution A and the solution B and stir to form a transparent sol;

[0031] S4. The transparent sol is dried at 150°C for 6 hours to obtain a solid powder;

[0032] S5. The solid powder is ball-milled for 2 hours and then calcined at 250°C for 2 hours under a hydrogen atmosphere.

[0033] S6. After cooling the calcined solid powder, ball mill it for 2 hours, and then calcin it again at 250°C for 2 hours under hydrogen atmosphere.

[0034] S6. The solid powder after secondary calcination is calcined at 800℃ in a nitrogen atmosphere for 4 hours, and finally calcined in a muffle furnace at 300℃ for 3 hours to obtain the solid single-atom catalyst Mn1 / CeO2-1.

[0035] The manganese loading in the solid-phase single-atom catalyst Mn1 / CeO2-1 was found to be 0.89 wt%.

[0036] Example 2

[0037] A method for synthesizing a solid-phase single-atom catalyst (Mn1 / CeO2-2) includes the following steps:

[0038] S1. Mix 3g of cerium nitrate and 0.2g of manganese nitrate, and then dissolve them in a 50% aqueous ethanol solution (ethanol to water in a 1:1 mass ratio) to obtain solution A, which is ready for use.

[0039] S2. Mix 1g of glycerol and 2g of citric acid monohydrate and dissolve them in a 50% ethanol aqueous solution (ethanol to water mass ratio of 1:1) to obtain solution B, which is then set aside.

[0040] S3. Mix the solution A and the solution B and stir to form a transparent sol;

[0041] S4. The transparent sol is dried at 150°C for 6 hours to obtain a solid powder;

[0042] S5. The solid powder is ball-milled for 2 hours and then calcined at 250°C for 2 hours under a hydrogen atmosphere.

[0043] S6. After cooling the calcined solid powder, ball mill it for 2 hours, and then calcin it again at 250°C for 2 hours under hydrogen atmosphere.

[0044] S6. The solid powder after secondary calcination is calcined at 800℃ in a nitrogen atmosphere for 4 hours, and finally calcined in a muffle furnace at 300℃ for 3 hours to obtain the solid single-atom catalyst Mn1 / CeO2-2.

[0045] The manganese loading in the solid-phase single-atom catalyst Mn1 / CeO2-2 was found to be 2.48 wt%.

[0046] Comparative Example 1

[0047] A type of MnO x The synthesis method of / CeO2 catalyst is as follows:

[0048] S1. Mix 3g of cerium nitrate and 0.1g of manganese nitrate, and then dissolve them in a 50% aqueous ethanol solution (ethanol to water in a 1:1 mass ratio) to obtain solution A, which is ready for use.

[0049] S2. Mix 1g of glycerol and 2g of citric acid monohydrate and dissolve them in a 50% ethanol aqueous solution (ethanol to water mass ratio of 1:1) to obtain solution B, which is then set aside.

[0050] S3. Mix the solution A and the solution B and stir to form a transparent sol;

[0051] S4. The transparent sol is dried at 150°C for 6 hours to obtain a solid powder;

[0052] S6. The solid powder was calcined at 800℃ in a nitrogen atmosphere for 4 hours, and finally calcined in a muffle furnace at 300℃ for 3 hours to obtain MnO.x / CeO2 catalyst.

[0053] Comparative Example 2

[0054] A method for synthesizing a CeO2 catalyst, comprising the following steps:

[0055] S1. Dissolve 3g of cerium nitrate in a 50% aqueous ethanol solution (ethanol to water in a 1:1 mass ratio) to obtain solution A, which is then set aside.

[0056] S2. Mix 1g of glycerol and 2g of citric acid monohydrate and dissolve them in a 50% ethanol aqueous solution (ethanol to water mass ratio of 1:1) to obtain solution B, which is then set aside.

[0057] S3. Mix the solution A and the solution B and stir to form a transparent sol;

[0058] S4. The transparent sol is dried at 150°C for 6 hours to obtain a solid powder;

[0059] S5. The solid powder is ball-milled for 2 hours and then calcined at 250°C for 2 hours under a hydrogen atmosphere.

[0060] S6. After cooling the calcined solid powder, ball mill it for 2 hours, and then calcin it again at 250°C for 2 hours under hydrogen atmosphere.

[0061] S6. The solid powder after secondary calcination is calcined at 800℃ in a nitrogen atmosphere for 4 hours, and finally calcined in a muffle furnace at 300℃ for 3 hours to obtain CeO2 catalyst.

[0062] Table 1. Rietveld refined structural parameters of CeO2 and catalysts from Examples 1-2

[0063]

[0064] Table 2 CeO2 and MnO x Rietveld refined structural parameters of / CeO2 catalyst

[0065]

[0066] In this invention, the dried solid powder is ball-milled and then calcined at 250°C for 2 hours in a reducing atmosphere, followed by another round of ball milling and calcination. This causes oxygen vacancies to form on the CeO2 surface, and correspondingly generates some localized electron-rich centers (CeO2). 3+During ball milling, these localized defect sites (electron-rich centers) anchor Mn species. The resulting solid particles are then subjected to high-temperature (800℃) pyrolysis calcination under an inert atmosphere. Manganese citrate decomposes upon heating, and the Mn produced from this pyrolysis is further anchored by electron-rich centers on the CeO2 surface, thus achieving atomic-level dispersion.

[0067] As can be seen from the XRD patterns of Mn1 / CeO2-1 and Mn1 / CeO2-2, the catalysts prepared in Examples 1-2 of this invention only show diffraction peaks of the cubic fluorite CeO2 structure, and no other diffraction peaks were found, indicating that no Mn-related nanoparticles were formed. Table 1-2, which shows the refinement parameters for each catalyst, also indicates that no severe lattice distortion was found in the catalysts prepared in Examples 1-2.

[0068] Comparative Example 1MnO x The XRD pattern of the / CeO2 catalyst shows that MnO x In addition to the diffraction peaks of the cubic fluorite CeO2, the / CeO2 catalyst also exhibits diffraction peaks of Mn2O3 and Mn3O4. According to ICP-AES analysis, the Mn loadings in the Mn1 / CeO2-1 and Mn1 / CeO2-2 catalysts are 0.89 wt.% and 2.48 wt.%, respectively.

[0069] The Mn1 / CeO2-2 single-atom catalyst was precisely characterized using aberration-corrected high-angle dark-field scanning transmission electron microscopy (AC-STEM HAADF). Figure 4 As can be seen from the data, the Mn1 / CeO2-2 catalyst mainly exposes the (111) crystal plane of CeO2. Figure 4 (a) Since the atomic numbers of Mn and Ce atoms are not significantly different, it is difficult to distinguish single Mn atoms by atomic contrast. However, the presence of Mn elements was confirmed by electron energy loss spectroscopy (EELS) analysis of the CeO2(111) crystal plane. Figure 4 (b) Further analysis of the valence state of Ce near the Mn single atom was conducted using EELS analysis. Figure 4 (c) shows the EELS spectra of the Ce M4 and M5 edges obtained in the surface region of the nanoparticles. (Compared to Ce) 3+ In comparison, Ce 4+ Edges M4 and M5 exhibit high energy loss. The intensity ratio between edges M4 and M5 can be used for Ce... 3+ With Ce 4+ Quantitative analysis, Ce 4+ and Ce 3+The M5 / M4 ratios are approximately 0.90 and 1.25, respectively. Calculations show that the strength ratio between the M4 and M5 edges of Mn1 / CeO2-2 is 1.13, which is higher than that of Ce2O3 (Ce...). 3+ ) 0.9 and lower than CeO2 (Ce 4+ The value of 1.25 indicates that the loading of Mn single atoms reduces the valence state of Ce near the Mn single atom, resulting in a mixed valence state of +3 and +4 Ce on the Mn1 / CeO2-2 surface. Figure 4 As shown in (d)-(g), the elemental diagrams obtained by energy dispersive X-ray spectroscopy (EDS) show that Mn, O, and Ce are uniformly distributed throughout the catalyst, with Mn being present in a small amount and exhibiting an isolated and uniform distribution.

[0070] The catalysts prepared in Examples 1-2 and Comparative Examples 1-2 were subjected to catalytic denitration tests. The specific denitration methods are as follows:

[0071] A self-designed and constructed fixed-bed reactor was used to test the performance of the catalyst in the NH3-SCR reaction, including the catalyst's catalytic activity and N2 selectivity. First, the prepared catalyst powder was pressed into tablets and sieved to 60-100 mesh. Then, it was placed in a reaction tube (8 mm inner diameter), and a thermocouple was inserted into the reaction tube to monitor the reaction temperature. The gas concentrations of the reactants were adjusted using flow meters, with NO at 500 ppm, NH3 at 500 ppm, O2 at 5 vol.%, and N2 as the balance gas. The reaction space velocity (GHSV) was set to 18,000, 30,000, or 50,000 h⁻¹ depending on the actual sample and experiment. 1 Once the reaction reached stability, NO, NO2, and O2 in the exhaust gas were recorded using a flue gas analyzer (Testo 355), while N2O and NH3 were recorded using a portable gas analyzer (GASMET FTIR DX4000). We are interested in the NO content of the reaction. x The conversion rate and selectivity of N2 are calculated using the following formulas:

[0072]

[0073]

[0074] Among them, [NO x ]-[NO]+[NO2].

[0075] from Figure 6 As can be seen from the above, when used as an NH3-SCR catalyst at different temperatures, the NO conversion and N2 selectivity are as follows: Figure 6As shown in (a) and (b), the low-temperature activity of the Mn1 / CeO2 single-atom catalyst is significantly better than that of CeO2. The highest NO conversion rate of the pure CeO2 catalyst is only 30%, however, with the loading of Mn single atoms, the NO conversion rate is significantly improved after Mn single atoms are loaded onto the CeO2 surface. Among all catalysts with different Mn loadings, the Mn1 / CeO2-2 catalyst exhibits the best catalytic activity, with its NO conversion rate remaining above 95% over a wide temperature range of 120℃ to 270℃.

[0076] Furthermore, the Mn1 / CeO2-2 catalyst also exhibits excellent N2 selectivity (>95%) over a wide temperature range. Mn1 / CeO2-1 exhibits lower catalytic performance due to its lower Mn single-atom loading and fewer active sites. This also illustrates the contribution of Mn single-atom sites to the catalytic activity of the Mn1 / CeO2 catalyst. However, for MnO... X / CeO2 catalyst, due to excessive Mn loading, because it leads to MnO X The generation of nanoparticles leads to the formation of Mn-Mn bonds, which in turn causes the peroxidation of NH3, resulting in a significant decrease in selectivity.

[0077] It should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and other modifications are possible. All modifications directly or indirectly derived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for synthesizing a solid-phase single-atom catalyst, characterized in that, The method comprises the following steps: S1, mixing 3g of cerium nitrate and 0.1g-0.2g of manganese nitrate, and then dissolving them in a mixed solution of ethanol and water to obtain solution A for standby; S2, mixing 1g of glycerol and 2g of citric acid monohydrate, and then dissolving them in a mixed solution of ethanol and water to obtain solution B for standby; S3, mixing the solution A and the solution B, and stirring to form a transparent sol; S4, drying the transparent sol at 150-180 ℃ for 6-8 h to obtain a solid powder; S5, ball-milling the solid powder and then calcining it at 250-270 ℃ for 2-3 h under a reducing atmosphere; S6, cooling the calcined solid powder, ball-milling it, and then calcining it at 250-270 ℃ for 2-3 h under a reducing atmosphere again; firing the solid powder after the second calcination at 800-1000 ℃ for 4-6 h in a nitrogen atmosphere, and finally firing it at 290-310 ℃ for 3-4 h in a muffle furnace to obtain a solid-phase single-atom catalyst.

2. The method of claim 1, wherein the solid single-atom catalyst is synthesized by a method comprising: The mass ratio of ethanol to water in steps S1 and S2 is 1:1-2:

1.

3. The method for synthesizing the solid-phase single-atom catalyst according to claim 1, characterized in that, The ball-milling time in steps S5 and S6 is 2-4 h.

4. The method of claim 1, wherein the solid single-atom catalyst is synthesized by a method comprising: The reducing atmosphere in steps S5 and S6 is hydrogen.

5. The method for synthesizing the solid-phase single-atom catalyst according to claim 1, characterized in that, The loading amount of manganese in the solid-phase single-atom catalyst is 0.89-2.48wt%.

Images