Silver-copper-cobalt ternary spinel type catalyst as well as preparation method and application thereof

Abstract

The invention discloses a silver-copper-cobalt ternary composite spinel type catalyst and a preparation method and application thereof, and belongs to the technical field of catalysts, and the prepared catalyst has good application in CO-SCR denitration of activated carbon regenerated flue gas. Aiming at the problem that a traditional catalyst is insufficient in activity under a low-temperature condition, the Ag0. 02Cu0. 98Co2O4 catalyst with a spinel structure is prepared by using a copper salt, a cobalt salt and a silver salt as precursors and combining citric acid-assisted mesoporous regulation and control under air calcination at 400 DEG C through an improved sol-gel method. The surface of the catalyst has abundant Ag < + >-Ov-Co < 3 + > asymmetric oxygen vacancies, the NOx conversion rate at 100 DEG C is higher than 85%, the NOx removal rate at 150 DEG C is close to 100%, and the catalyst has excellent low-temperature denitration activity. The problem that the CO-SCR technology is low in activity under the low-temperature condition is solved, an efficient solution is provided for pollution reduction and carbon reduction of activated carbon regeneration flue gas, and the method has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a silver-copper-cobalt ternary composite spinel catalyst, a preparation method and an application thereof. Background Art

[0002] Ozone pollution has become a key bottleneck restricting the continuous improvement of my country's air quality. Its key precursor, nitrogen oxides (NO x ) requires further breakthroughs in deep emission reduction. Although the selective catalytic reduction technology (NH3-SCR) using ammonia as a reducing agent has been industrialized, it still faces technical bottlenecks such as ammonia slip and sulfur poisoning. It is worth noting that non-electric industries (metallurgy, waste incineration, etc.) and mobile sources (motor vehicles, ships, etc.) as NO x A typical emission source, its flue gas components are characterized by the coexistence of NO and CO. To address this characteristic, the development of selective catalytic reduction technology (CO-SCR) using CO as a reducing agent not only achieves the synergistic removal of NO and CO, but also offers the dual advantages of "treating waste with waste" and "reducing pollution and carbon emissions."

[0003] Activated carbon denitrification is widely used in the metallurgical industry. The activated carbon regeneration process is an important part of the flue gas purification system. While realizing the recycling of adsorbents, the flue gas released during the regeneration process contains high concentrations of NO. x , and efficient denitrification treatment is urgently needed. The temperature of the activated carbon regenerated flue gas after waste heat recovery is mostly at 80-180℃, and the NO conversion rate of traditional catalysts in this low temperature zone is less than 30%, and the high temperature section (>220℃) is inefficient or even deactivated due to excessive oxidation of CO, which has become one of the main obstacles to the industrial application of this technology. In recent years, transition metals (Fe, Mn, Cu, etc.) have been widely used in CO-SCR research due to their high catalytic activity and low economic cost. For example, CuCo2O4 spinel catalyst has a NO conversion rate of less than 30% at 100℃. x The conversion rate is about 50%, but its low-temperature activity (<150°C) still needs to be further improved.

[0004] Therefore, developing CO-SCR catalysts that operate at low temperatures has become a critical technical bottleneck in this field. Substitution at the A-site in spinel catalysts can simultaneously modulate both the oxygen vacancy concentration and the electronic state of the metal active centers, offering a new approach to addressing this issue. This study restructured the surface oxygen species distribution of CuCo₂O₄ by noble metal doping, enhancing catalytic activity at low temperatures. Summary of the Invention

[0005] The present invention aims to address the shortcomings of existing technologies by providing a silver-copper-cobalt ternary composite spinel catalyst, its preparation method, and its application. This invention utilizes an improved sol-gel method to prepare a spinel-structured silver-copper-cobalt ternary catalyst, addressing the deactivation issue of conventional CO-SCR catalysts under low-temperature, oxygen-containing conditions.

[0006] To achieve the above technical problems, the first aspect of the present invention provides a method for preparing a silver-copper-cobalt ternary composite spinel catalyst, comprising the following steps:

[0007] Step (1), taking copper salt, cobalt salt, silver salt and citric acid, dissolving them in ethanol aqueous solution, and stirring them thoroughly until they are completely dissolved to obtain a mixed solution;

[0008] Step (2), evaporating the solvent of the mixed solution obtained in step (1) to obtain a viscous sol;

[0009] Step (3), drying the viscous sol obtained in step (2) to obtain a fluffy dry glue;

[0010] Step (4): placing the fluffy dry glue obtained in step (3) in a tubular furnace and calcining it to obtain a silver-copper-cobalt ternary spinel catalyst.

[0011] Furthermore, in step (1), the molar ratio of silver salt to copper salt is 1:50-1:30, the molar ratio of (copper salt + silver salt) to cobalt salt is 1:2; the molar ratio of citric acid to total metal ions is 0.5-1:1, and the concentration of ethanol aqueous solution is 10-50wt.%; preferably, the molar ratio of citric acid to total metal ions is 1:1.

[0012] Furthermore, the copper salt is copper nitrate or copper acetate; the cobalt salt is cobalt nitrate or cobalt acetate; the silver salt is nitrate or silver acetate; preferably, the copper salt is copper nitrate; the cobalt salt is cobalt nitrate; and the silver salt is silver nitrate.

[0013] Furthermore, in step (2), the temperature for evaporating the solvent is 60-90°C, preferably 80°C.

[0014] Furthermore, in step (3), the drying condition is 80-150° C. for 0.5-1 h, preferably 150° C. for 1 h.

[0015] Furthermore, in step (4), the calcination conditions in the tubular furnace are 300-400°C in an air atmosphere, calcination for 2-4 hours, and a heating rate of 1-2°C / min; preferably, the calcination conditions in the tubular furnace are 400°C in an air atmosphere, calcination for 4 hours.

[0016] Preferably, 0.02 mmol of AgNO₃ is dissolved in 20 mL of a 20 wt.% aqueous ethanol solution and stirred. Then, 0.98 mmol of Cu(NO₃)₂·3H₂O and 2 mmol of Co(NO₃)₂·6H₂O are dissolved in this solution at room temperature. The corresponding amount of citric acid is then added to the resulting solution, maintaining a molar ratio of citric acid to total metal ions of 1:1. Stirring is continued for 30 minutes to completely dissolve the drug. The solution is then gradually heated to 80°C with continuous stirring to completely evaporate the water, forming a gel. The resulting gel is dried in a forced-air drying oven at 120°C for 1 hour, then calcined in a tube furnace at 400°C in an air atmosphere for 3 hours at a heating rate of 2°C / min.

[0017] The second aspect of the present invention is a silver-copper-cobalt ternary composite spinel catalyst prepared by the preparation method.

[0018] The third aspect of the present invention is the application of the silver-copper-cobalt ternary composite spinel catalyst prepared by the preparation method in CO-SCR denitrification.

[0019] Furthermore, the chemical formula of the catalyst is Ag 0.02 Cu 0.98 Co2O4, the silver-copper-cobalt ternary composite spinel catalyst improves the low-temperature activity of CO-SCR, and the catalyst has a low temperature of NO when the reaction temperature is 150 ° C. x The removal rate of NO is about 99%; when the reaction temperature is 100℃, the catalyst x The removal rate reaches about 88%, with excellent low-temperature denitrification activity.

[0020] The fourth aspect of the present invention is the application of the silver-copper-cobalt ternary composite spinel catalyst prepared by the preparation method in activated carbon regeneration flue gas denitrification.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention adopts an improved sol-gel method to prepare a silver-copper-cobalt ternary catalyst. The obtained catalyst maintains a spinel structure and has a more uniform particle size distribution, abundant asymmetric oxygen vacancies (Ag + -O v -Co 2+ When the prepared silver-copper-cobalt ternary spinel catalyst was applied to activated carbon regeneration flue gas denitrification, the low-temperature activity of CO-SCR was improved, and the efficiency of CO-SCR was improved. In particular, compared with other composite catalysts (Pd / Ru / Pt), the silver-copper-cobalt catalyst had significantly higher NO x removal efficiency and CO conversion rate. The catalyst obtained has a NO xThe removal rate of NO is close to 100%. When the reaction temperature is 100℃, x The removal rate reaches about 88%, with excellent low-temperature denitrification activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The catalysts prepared in Examples and Comparative Examples 1-4 were subjected to NO x Conversion rate graph;

[0024] Figure 2 Graph showing the CO conversion rates of the catalysts prepared in Examples and Comparative Examples 1-4 under oxygen-free conditions;

[0025] Figure 3 The XRD patterns of the catalysts prepared in Examples and Comparative Examples 1-4 are shown;

[0026] Figure 4 The Raman spectra of the catalysts prepared in Examples and Comparative Examples 1-4 are shown;

[0027] Figure 5 In the figure, (a) is a N2 adsorption-desorption diagram of the catalysts prepared in Examples and Comparative Examples 1-4, and (b) is a pore size distribution diagram of the catalysts prepared in Examples and Comparative Examples 1-4;

[0028] Figure 6 TEM images of the catalysts prepared in Examples and Comparative Examples 1-4, wherein (a) is a microscopic morphology image of Comparative Example 1; (b) is a particle size distribution image of Comparative Example 1; (c) is a lattice fringe image of Comparative Example 1; (d) is a microscopic morphology image of the Example; (e) is a particle size distribution image of the Example; and (f) is a lattice fringe image of the Example.

[0029] Figure 7 The O1s XPS graphs of the catalysts prepared in Examples and Comparative Examples 1-4 are shown. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in detail below through specific embodiments, but the protection scope of the present invention is not limited to the embodiments.

[0031] Example 1 Preparation of Silver-Copper-Cobalt Ternary Catalyst

[0032] Weigh 0.02mmol AgNO3 and dissolve it in 20ml of 20wt.% ethanol aqueous solution and stir. Then, dissolve 0.98mmol Cu(NO3)2·3H2O and 2mmol Co(NO3)2·6H2O in the solution at room temperature. Add the corresponding amount of citric acid to the resulting solution so that the molar ratio of citric acid to total metal ions remains at 1 / 1. Stir continuously for 30 minutes to completely dissolve the drug. Then gradually heat the above solution to 80℃ and continue stirring to completely evaporate the water to form a gel. Place the obtained gel in a forced air drying oven at 120℃ and dry it for 1h. Then place it in a tube furnace and calcine at 400℃ in an air atmosphere for 3h with a heating rate of 2℃ / min.

[0033] The obtained samples were subjected to CO-SCR denitrification performance test. The catalytic activity test method was as follows: the catalyst was sieved to 40-60 mesh and placed in a quartz reaction tube. The simulated reaction gas composition was 1000ppm CO and 500ppm NO. x , the balance gas is N2, and the volume space velocity is 50000h -1 The NO concentration at the inlet and outlet was detected by a nitrogen oxide analyzer (Thermal Fisher 42i-LH), and the CO concentration was measured by gas chromatography (Folley GC9790II). x The removal rate is close to 100%.

[0034] NO x The test results of conversion rate and CO conversion rate are as follows: Figure 1 and Figure 2 As shown, it can be seen that at 125℃, NO x The conversion rate reaches about 97%, which is better than other catalysts. Figure 3 As shown, the CO conversion rate remains relatively high throughout the entire test temperature range, reaching approximately 100% at 250°C. The test results demonstrate that the silver-copper-cobalt ternary catalyst has excellent low-temperature denitrification performance and is also effective in removing CO.

[0035] Comparative Example 1 Preparation of Copper-Cobalt Binary Catalyst

[0036] Weigh 1mmol Cu(NO3)2·3H2O and 2mmol Co(NO3)2·6H2O into 20ml of 20wt.% ethanol aqueous solution and stir until fully dissolved; weigh citric acid and add it to the above mixed solution, stir until fully dissolved; heat the above solution to 80°C and stir continuously to evaporate the water completely, until the solvent of the mixed solution is initially evaporated to obtain a viscous colloidal substance, then place it in a 120°C oven and dry it for 1h to obtain a fluffy dry glue, grind the dry glue into powder, place it in a tubular furnace at 400°C in air atmosphere and calcine for 3h, and the heating rate during calcination in the tubular furnace is 2°C / min, to obtain a copper-cobalt binary catalyst sample.

[0037] Comparative Example 2 Preparation of palladium copper cobalt ternary catalyst

[0038] Weigh 0.02 mmol PdCl2 and dissolve it in 20 ml of 20 wt.% ethanol aqueous solution and stir until fully dissolved; weigh citric acid and add it to the above mixed solution, stir until fully dissolved; heat the above solution to 80°C and stir continuously to evaporate the water completely, until the solvent of the mixed solution is initially evaporated to obtain a viscous colloidal substance, then place it in a 120°C oven and dry it for 1 hour to obtain a fluffy dry glue, grind the dry glue into powder, place it in a tubular furnace at 400°C in an air atmosphere and calcine for 3 hours. The heating rate during calcination in the tubular furnace is 2°C / min, and a palladium-copper-cobalt ternary catalyst sample can be obtained.

[0039] Comparative Example 3 Preparation of Platinum-Copper-Cobalt Ternary Catalyst

[0040] Weigh 0.02mmol H2PtCl6 and dissolve it in 20wt.% ethanol aqueous solution and stir until fully dissolved; weigh citric acid and add it to the above mixed solution, stir until fully dissolved; heat the above solution to 80℃ and stir continuously to evaporate the water completely, until the solvent of the mixed solution is initially evaporated to obtain a viscous colloidal substance, then place it in a 120℃ oven and dry it for 1h to obtain a fluffy dry glue, grind the dry glue into powder and place it in a tubular furnace at 400℃ in air atmosphere for calcination for 3h. The heating rate during calcination in the tubular furnace is 2℃ / min, and a platinum-copper-cobalt ternary catalyst sample can be obtained.

[0041] Comparative Example 4 Preparation of Ruthenium-Copper-Cobalt Ternary Catalyst

[0042] 0.02 mmol of RuCl3 was dissolved in a 20 wt.% aqueous ethanol solution and stirred until fully dissolved; citric acid was weighed and added to the mixed solution, and stirred until fully dissolved; the solution was heated to 80°C and stirred continuously to completely evaporate the water, until the solvent in the mixed solution was initially evaporated to obtain a viscous colloidal substance, which was then placed in a 120°C oven and dried for 1 hour to obtain a fluffy dry glue, which was ground into powder and calcined in an air atmosphere in a tubular furnace at 400°C for 3 hours. The heating rate during calcination in the tubular furnace was 2°C / min, and a ruthenium-copper-cobalt ternary catalyst sample was obtained.

[0043] Figure 1 The NO of the catalysts prepared in Examples and Comparative Examples 1-4 is x Conversion rate diagram. It was found that doping with Ag, Pd and Ru can significantly increase NO x conversion rate. Especially when Ag doped at 100℃, NO x The conversion rate increased by about 39%. x The conversion rate is about 85%, and above 150℃, NO x The conversion rate is higher than 95%. Pt doping significantly reduces NO x Conversion rate, NO at 250℃ x Only reached about 90%.

[0044] Figure 2 The CO conversion rate of the catalysts prepared in Examples and Comparative Examples 1-4 is shown in Figure 2. Similarly, doping with Ag, Pd and Ru also increases the CO conversion of NO. x Conversion rate. Compared with CuCo2O4 catalyst, the CO conversion rate after Ag doping increased by about 10-20% between 100-150℃ and remained close to 100% above 200℃. 90 (Temperature at 90% conversion) dropped by about 42°C.

[0045] Figure 3 The XRD patterns of the catalysts prepared in Examples and Comparative Examples 1-4 are shown. For the CuCo2O4 catalyst, the diffraction peaks at 2θ of 19.03°, 31.31°, 36.90°, 38.59°, 44.88°, 55.73°, 59.43°, 65.34° and 77.47° are respectively attributed to (Cu 0.30 Co 0.70)Co2O4 (JCPDS PDF#25-0270) (111), (220), (311), (222), (400), (422), (511), (440) and (533) crystal planes. In addition, the (11-1), (200) and (20-2) crystal planes belonging to CuO (PDF#48-1548) were observed at 35.69°, 38.89° and 49.00°, indicating the presence of a small amount of CuO impurities in the sample. This may be due to incomplete reaction or partial decomposition of the CuCo2O4 catalyst during calcination. When the noble metal was introduced, the position of the main diffraction peak did not change significantly, but the peak intensity did change, indicating that doping did not change the crystal structure of the CuCo2O4 catalyst, but changed its crystallinity. According to the Scherrer equation, Ru and Ag doping reduces the grain size of CoCu2O4, while Pd and Ru doping increases its grain size. In addition, it is noted that the diffraction peaks attributed to the (311) crystal plane shift after doping. Among them, after doping with Ag and Pd, the diffraction peaks shift to smaller angles, while after doping with Pt, the diffraction peaks shift to larger angles. This is because Cu 2+ The ionic radius (0.073nm) is smaller than that of Ag + (0.115nm) and Pd 2+ (0.086nm), but larger than Pt 4+ This indicates that the CuCo2O4 catalyst has undergone lattice distortion. At the same time, no diffraction peaks of the corresponding metal state and oxide were observed, which suggests that the noble metal has been successfully doped into the CuCo2O4 spinel unit cell.

[0046] Figure 4 The Raman spectra of the catalysts prepared in Example and Comparative Examples 1-4 are shown. Three Raman modes belonging to the spinel Fd-3m space group were detected in the CuCo2O4 sample, namely A 1g 、E g and F 2g . Located at 193 and 507cm -1 The peak corresponds to F 2g Vibration mode, located at 468cm -1 The peak at corresponds to E g Vibration mode, located at 666cm -1 The peak at corresponds to A 1g Vibration mode. 590cm -1 The peak at belongs to the B of CuO 2g vibration mode, which is consistent with the XRD results. Located at 193cm -1 The Raman peak at 666cm is attributed to the Cu tetrahedral site (CuO4). The peak intensity and peak position of the catalyst shifted after doping, which proves that the doped metal ions replaced some copper ions.-1 The Raman peak at the Co octahedral site (CoO6) also observed a shift and peak height change, which is speculated to be due to the M n+ -O-Co 3+ The formation of the new coordination structure changes the electronic structure of the Co-O bond.

[0047] Figure 5 The N2 adsorption-desorption diagram of the catalysts prepared in Examples and Comparative Examples 1-4 is shown. The isotherms of all catalysts are still IV type, indicating that the doping of precious metals has almost no effect on the pore structure. Combined with the pore size distribution diagram, it can be seen that the pore size distribution of the catalysts is mainly mesopores between 5 and 20 nm. The specific surface areas of CuCo2O4, Ag-CuCo2O4, Pd-CuCo2O4, Ru-CuCo2O4, and Pt-CuCo2O4 catalysts are 34.0, 30.1, 37.5, and 41.9 m2, respectively. 2 / g, 37.2m 2 / g. Ag doping reduced the specific surface area and pore volume of the catalyst, while Pd, Pt, and Ru doping increased their specific surface area and pore volume. This suggests that changes in the catalyst's chemical properties are the primary reason for its enhanced CO-SCR activity.

[0048] Figure 6 TEM images of the catalysts prepared in Examples and Comparative Examples 1-4. The grain sizes of CuCo2O4 and Ag-CuCo2O4 catalysts are mainly distributed between 10 and 14 nm, which is close to the grain size calculated by XRD. The average grain size of Ag-CuCo2O4 is 10.0 nm, which is smaller than the average grain size of CuCo2O4 of 11.9 nm, indicating that Ag doping reduces the grain size of the CuCo2O4 catalyst. The CuCo2O4 catalyst is mainly observed to correspond to the (311), (111) and (222) crystal planes. In contrast, Ag doping did not change the main exposed crystal planes of the catalyst. However, it should be noted that obvious lattice distortion was observed on the (311) crystal plane of Ag-CuCo2O4, which directly proves that the Ag ions were successfully doped into the lattice of the CuCo2O4 catalyst.

[0049] Figure 7 The XPS graphs of O1s of the catalysts prepared in Examples and Comparative Examples 1-4 are shown. The high-resolution spectrum of O1s can be fitted into two peaks: the adsorbed oxygen (denoted as O1s) at 531.0-531.4 eV. α ) and lattice oxygen (denoted as O) at 529.4~529.8eV β ). α / (O) ratio can be used to reflect the relative content of oxygen vacancies. α / (O) ratio increased to 58%. In comparison, after Pt doping, Oα / (O α +O β ) ratio decreased to 39%. In addition, it was noted that the lattice oxygen binding energy of Ag-CuCo2O4 and Ru-CuCo2O4 shifted lower than that of CuCo2O4, indicating that the surface lattice oxygen electron density decreased with Ag doping, which is beneficial to improving its mobility.

[0050] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A method for preparing a silver-copper-cobalt ternary composite spinel catalyst, characterized in that: The following steps are involved: (1) Take copper salt, cobalt salt, silver salt and citric acid, dissolve them in ethanol aqueous solution, and stir them thoroughly until they are completely dissolved to obtain a mixed solution; (2) evaporating the solvent of the mixed solution obtained in step (1) to obtain a viscous sol; (3) drying the viscous sol obtained in step (2) to obtain a fluffy dry glue; (4) The fluffy dry glue obtained in step (3) is placed in a tubular furnace and calcined to obtain a silver-copper-cobalt ternary spinel catalyst.

2. The method for preparing the silver-copper-cobalt ternary composite spinel catalyst according to claim 1, characterized in that: In step (1), the molar ratio of silver salt to copper salt is 1:50-1:30, and the molar ratio of (copper salt + silver salt) to cobalt salt is 1:2; the molar ratio of citric acid to total metal ions is 0.5-1:1, and the concentration of the ethanol aqueous solution is 10-50wt.%; preferably, the molar ratio of citric acid to total metal ions is 1:

1.

3. The method for preparing the silver-copper-cobalt ternary composite spinel catalyst according to claim 1, characterized in that: The copper salt is copper nitrate or copper acetate; the cobalt salt is cobalt nitrate or cobalt acetate; the silver salt is nitrate or silver acetate; preferably, the copper salt is copper nitrate; the cobalt salt is cobalt nitrate; and the silver salt is silver nitrate.

4. The method for preparing the silver-copper-cobalt ternary composite spinel catalyst according to claim 1, characterized in that: In step (2), the temperature for evaporating the solvent is 60-90°C, preferably 80°C.

5. The method for preparing the silver-copper-cobalt ternary composite spinel catalyst according to claim 1, characterized in that: In step (3), the drying condition is 80-150° C. for 0.5-1 h, preferably 150° C. for 1 h.

6. The method for preparing the silver-copper-cobalt ternary composite spinel catalyst according to claim 1, characterized in that: In step (4), the calcination conditions in the tubular furnace are 300-400° C. in an air atmosphere, calcination for 2-4 h, and a heating rate of 1-2° C. / min; preferably, the calcination conditions in the tubular furnace are 400° C. in an air atmosphere, calcination for 4 h.

7. A silver-copper-cobalt ternary composite spinel catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the silver-copper-cobalt ternary composite spinel catalyst prepared by the preparation method according to claim 7 in CO-SCR denitrification.

9. Use of the catalyst according to claim 8, characterized in that The chemical formula of the catalyst is Ag 0.02 Cu 0.98 Co2O4, the silver-copper-cobalt ternary composite spinel catalyst improves the low-temperature activity of CO-SCR, and the catalyst has a low temperature of NO when the reaction temperature is 150 ° C. x The removal rate of NO is higher than 98%; when the reaction temperature is 100℃, the catalyst x The conversion rate is higher than 85%.

10. Use of the silver-copper-cobalt ternary composite spinel catalyst prepared by the preparation method according to claim 7 in activated carbon regeneration flue gas denitrification.

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