COPPER-PALLADIUM-LOADED MESOPOROUS SILICON CARBIDE-BASED CATALYST, PREPARATION METHOD AND APPLICATION THEREOF

Abstract

A copper-palladium-loaded mesoporous silicon carbide-based catalyst, a preparation method, and an application thereof are provided. First, a mesoporous silicon carbide material is prepared by using mesoporous silica as a hard template; subsequently, the mesoporous silicon carbide material is mixed with a copper-palladium precursor mixed solution, and dried after the solvent is completely volatilized. The dried powder is successively subjected to calcination with N.sub.2 and reduction with H.sub.2 to finally obtain the copper-palladium-loaded mesoporous silicon carbide-based catalyst. The catalyst is made into an electrode, and the nitrate in water body is catalytically reduced by electrochemical method. The preparation method of the catalyst of the present invention is simple. The catalyst can realize high-efficiency catalytic denitrification at a low metal loading amount, with high selectivity of nitrogen. Moreover, the catalyst has the advantages of high activity, good stability, wide application range and low cost.

Claims

1. A method for preparing a copper-palladium-loaded mesoporous silicon carbide-based catalyst, comprising the following steps: S1. mixing and stirring P123, water, hydrochloric acid, and tetraethyl orthosilicate to obtain a homogeneous solution; stirring the homogeneous solution in a water bath for crystallization to obtain a crystallized solution, then performing a first treatment of cooling, filtering, drying and calcination on the crystallized solution to obtain mesoporous silica; S2. dissolving polycarbosilane in xylene to obtain a polycarbosilane solution, wherein a number-average molecular weight of the polycarbosilane is 1500-2500; mixing and stirring the mesoporous silica and the polycarbosilane solution to obtain a first mixture, drying the first mixture after the xylene is completely volatilized to obtain first dried powder, and then subjecting the first dried powder to a second treatment of calcination, etching, washing and drying to obtain mesoporous silicon carbide; S3. mixing PdCl.sub.2 and Cu(NO.sub.3).sub.2.3H.sub.2O to obtain a copper-palladium precursor mixed solution; and S4. adding the mesoporous silicon carbide to the copper-palladium precursor mixed solution to obtain a second mixture, drying the second mixture after a solvent of the second mixture is completely volatilized to obtain second dried powder, and then subjecting the second dried powder to a third treatment of calcination in a nitrogen atmosphere and reduction in a hydrogen atmosphere to obtain the copper-palladium-loaded mesoporous silicon carbide-based catalyst.

2. The method according to claim 1, wherein in step S1, 2 g of the P123, 63.95 mL of the water, and 10 mL of the hydrochloric acid are mixed and stirred to obtain a first mixed solution, and 4.25 g of the tetraethyl orthosilicate is added dropwise to the first mixed solution to obtain the homogeneous solution.

3. The method according to claim 1, wherein in step S1, the crystallization is performed at a temperature of 130° C. for 72 hours; and the calcination of the first treatment is performed for 6 hours under conditions of an air atmosphere, a required temperature of 550° C., and a heating rate of 1° C./min.

4. The method according to claim 1, wherein a concentration of the polycarbosilane in the polycarbosilane solution is 10 wt %, and the mesoporous silica and the polycarbosilane solution are mixed in a mass ratio of 1:(1-1.2).

5. The method according to claim 1, wherein in step S2: a drying temperature is 80° C., and a drying time is 12 hours; and the etching is to mix and stir the first dried powder with an excess of 4 wt % HF aqueous solution for 24 hours.

6. The method according to claim 1, wherein, the calcination in step S2 is as follows: in a nitrogen atmosphere, first, raising a temperature of the first dried powder to 350° C. at a rate of 2° C./min, and keeping the temperature at 350° C. for 5 hours; then raising the temperature to 700° C. at a rate of 0.5° C./min; and then raising the temperature to 1200° C.-1400° C. at the rate of 2° C./min, and keeping the temperature at 1200° C.-1400° C. for 2 hours; finally, naturally cooling the first dried powder to room temperature under a protection of nitrogen.

7. The method according to claim 1, wherein in the copper-palladium precursor mixed solution: a mass concentration of palladium is 0.1-5 g/L; a mass concentration of copper is 0.05-2.5 g/L; and a mass ratio of the palladium to the copper is 2:1.

8. The method according to claim 1, wherein in step S4: a mass concentration of the mesoporous silicon carbide in the copper-palladium precursor mixed solution is 100 g/L; a drying temperature is 80° C., and a drying time is 12 hours; and conditions for the calcination and the reduction of the third treatment are as follows: a required temperature is 400° C., and a heating rate is 1° C./min; a time for the calcination in the nitrogen atmosphere is 3 hours, and a time for the reduction in the hydrogen atmosphere is 1 hour.

9. A copper-palladium-loaded mesoporous silicon carbide-based catalyst, wherein the copper-palladium-loaded mesoporous silicon carbide-based catalyst is prepared by using the method according to claim 1.

10. A method of using the copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, comprising: using the palladium-copper-loaded mesoporous silicon carbide-based catalyst as a working electrode, a platinum electrode as a counter electrode, and a saturated calomel electrode as a reference electrode; and placing the working electrode, the counter electrode and the reference electrode in a nitrate solution to obtain an electrocatalytic system for a denitrification reaction; wherein a time of the denitrification reaction is 24 hours, a temperature of the denitrification reaction is room temperature, and a voltage of the working electrode is −1.5 V; wherein in the nitrate solution, a NO.sub.3.sup.−—N concentration is 100-500 mg/L, and an initial pH is 3-11; and in the electrocatalytic system: a volume of the nitrate solution is 20 mL, and a mass of the copper-palladium-loaded mesoporous silicon carbide-based catalyst is 4 mg.

11. The method according to claim 2, wherein in step S1, the crystallization is performed at a temperature of 130° C. for 72 hours; and the calcination of the first treatment is performed for 6 hours under conditions of an air atmosphere, a required temperature of 550° C., and a heating rate of 1° C./min.

12. The method according to claim 4, wherein in step S2: a drying temperature is 80° C., and a drying time is 12 hours; and the etching is to mix and stir the first dried powder with an excess of 4 wt % HF aqueous solution for 24 hours.

13. The copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, wherein in step S1, 2 g of the P123, 63.95 mL of the water, and 10 mL of the hydrochloric acid are mixed and stirred to obtain a first mixed solution, and 4.25 g of the tetraethyl orthosilicate is added dropwise to the first mixed solution to obtain the homogeneous solution.

14. The copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, wherein in step S1, the crystallization is performed at a temperature of 130° C. for 72 hours; and the calcination of the first treatment is performed for 6 hours under conditions of an air atmosphere, a required temperature of 550° C., and a heating rate of 1° C./min.

15. The copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, wherein a concentration of the polycarbosilane in the polycarbosilane solution is 10 wt %, and the mesoporous silica and the polycarbosilane solution are mixed in a mass ratio of 1:(1-1.2).

16. The copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, wherein in step S2: a drying temperature is 80° C., and a drying time is 12 hours; and the etching is to mix and stir the first dried powder with an excess of 4 wt % HF aqueous solution for 24 hours.

17. The copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, wherein, the calcination in step S2 is as follows: in a nitrogen atmosphere, first, raising a temperature of the first dried powder to 350° C. at a rate of 2° C./min, and keeping the first temperature at 350° C. for 5 hours; then raising the temperature to 700° C. at a second rate of 0.5° C./min; and then raising the temperature to 1200° C.-1400° C. at the rate of 2° C./min, and keeping the temperature at 1200° C.-1400° C. for 2 hours; finally, naturally cooling the first dried powder to room temperature under a protection of nitrogen.

18. The copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, wherein in the copper-palladium precursor mixed solution: a mass concentration of palladium is 0.1-5 g/L; a mass concentration of copper is 0.05-2.5 g/L; and a mass ratio of the palladium to the copper is 2:1.

19. The copper-palladium-loaded mesoporous silicon carbide-based catalyst according to claim 9, wherein in step S4: a mass concentration of the mesoporous silicon carbide in the copper-palladium precursor mixed solution is 100 g/L; a drying temperature is 80° C., and a drying time is 12 hours; and conditions for the calcination and the reduction of the third treatment are as follows: a required temperature is 400° C., and a heating rate is 1° C./min; a time for the calcination in the nitrogen atmosphere is 3 hours, and a time for the reduction in the hydrogen atmosphere is 1 hour.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows a scanning electron microscope (SEM) image of a copper-palladium-loaded mesoporous silicon carbide-based material in embodiment 1 of the present invention;

[0018] FIG. 2 shows a scanning electron microscope (SEM) image of a copper-palladium-loaded mesoporous silicon carbide-based material in embodiment 2 of the present invention;

[0019] FIG. 3 shows a scanning electron microscope (SEM) image of a copper-palladium-loaded mesoporous silicon carbide-based material in embodiment 3 of the present invention;

[0020] FIG. 4 shows a transmission electron microscope (TEM) image of a copper-palladium-loaded mesoporous silicon carbide-based material in embodiment 1 of the present invention;

[0021] FIG. 5 shows a transmission electron microscope (TEM) image of a copper-palladium-loaded mesoporous silicon carbide-based material in embodiment 2 of the present invention;

[0022] FIG. 6 shows a transmission electron microscope (TEM) image of a copper-palladium-loaded mesoporous silicon carbide-based material in embodiment 3 of the present invention;

[0023] FIG. 7 shows removal rates of nitrate nitrogen (NO.sub.3.sup.−—N) and a selectivity of product nitrogen in catalytic reaction systems of a catalyst in embodiment 1, a catalyst in embodiment 2, a catalyst in embodiment 3 of the present invention and a catalyst in the prior art comparative example;

[0024] FIG. 8 shows a removal rate of nitrate nitrogen (NO.sub.3.sup.−—N) and a selectivity of product nitrogen of the catalyst in a neutral reaction system with a NO.sub.3.sup.−—N concentration of 100-500 mg/L in embodiment 1 of the present invention; and

[0025] FIG. 9 shows a removal rate of nitrate nitrogen (NO.sub.3.sup.−—N) and a selectivity of product nitrogen of the catalyst in a reaction system with a NO.sub.3.sup.−—N concentration of 100 mg/L and an initial pH of 3-11 in embodiment 1 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Hereinafter, referring to the attached figures of the embodiments of the present invention, the present invention is described in more detail below. It is worth noting that the present invention can be implemented in many different forms and shall not be limited by the embodiments presented herein. On the contrary, these embodiments are presented to achieve a full and complete disclosure and to enable those skilled in this field to fully understand the protective scope of the present invention. In these figures, the dimensions and relative dimensions of layers and regions may have been enlarged for clarity.

[0027] The following illustration is made with three embodiments and a prior art comparative example.

[0028] Embodiment 1, a preparation method of a palladium-copper-loaded mesoporous silicon carbide-based catalyst, which includes the steps as follows.

[0029] (1) 2 g of surfactant P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide, PEO-PPO-PEO), 63.95 mL of deionized water and 10 mL of hydrochloric acid (12 M) were taken and put into a beaker, stirred until completely dissolved, and 4.25 g of tetraethyl orthosilicate (TEOS) was subsequently added dropwise to the beaker. A mechanical stirring was performed in a 40° C. water bath for 24 hours, and then the solution in the beaker was poured into a stainless-steel autoclave. Subsequently, the stainless-steel autoclave was placed in a 130° C. oven for static crystallization for 72 hours, followed by being subjected to cooling, filtering, drying and then calcining in a 550° C. muffle furnace for 6 hours to obtain mesoporous silica.

[0030] (2) 5 g of the mesoporous silica was taken and added to a 10 wt % xylene solution of polycarbosilane containing 6 g of the polycarbosilane, mixed and stirred until the xylene was completely volatilized, and then placed in an 80° C. oven for drying for 12 hours. After drying, the dried powder was placed in a tube furnace and calcined in a nitrogen atmosphere. In the tube furnace, the temperature was first raised to 350° C. at a rate of 2° C./min and kept for 5 hours, then raised to 700° C. at a rate of 0.5° C./min, and then raised to 1400° C. at a rate of 2° C./min and kept for 2 hours, and finally the dried powder was naturally cooled to room temperature under nitrogen protection. The cooled powder was taken and added to an excess of 4 wt % HF aqueous solution, stirred at room temperature for 24 hours, and then subjected to repeated washing, filtering, and drying to obtain mesoporous silicon carbide. The drying condition was 80° C. and the drying time was 12 hours.

[0031] (3) PdCl.sub.2 and Cu(NO.sub.3).sub.2.3H.sub.2O were mixed to obtain a copper-palladium precursor mixed solution. In the copper-palladium precursor mixed solution, a mass concentration of the palladium is 0.1 g/L; a mass concentration of the copper is 0.05 g/L.

[0032] (4) 1 g of the mesoporous silicon carbide was taken and added to 10 mL of the copper-palladium precursor mixed solution, mixed and stirred until the solvent was completely volatilized, dried in an 80° C. oven for 12 hours, and then placed in a tube furnace. The temperature was raised to 400° C. at a rate of 1° C./min for calcination in a nitrogen atmosphere for 3 hours and reduction in a hydrogen atmosphere for 1 hour to obtain a mesoporous silicon carbide-based catalyst loaded with palladium (0.1%) and copper (0.05%). The surface morphology of the mesoporous silicon carbide-based catalyst loaded with palladium and copper is shown in FIG. 1 and FIG. 4.

[0033] 4 mg of the mesoporous silicon carbide-based catalyst loaded with palladium (0.1%) and copper (0.05%) was taken and coated on a nickel foam to make a working electrode, a platinum electrode was used as a counter electrode, and a saturated calomel electrode was used as a reference electrode. The three electrodes were placed in a neutral solution with a volume of 20 mL and a NO.sub.3.sup.−—N concentration of 100 mg/L, and a voltage of −1.5 V was applied for reaction for 24 hours. Subsequently, the concentration of the nitrate was measured after the reaction, and the removal rate of the nitrate and the selectivity of the nitrogen were calculated. The results are shown in FIG. 7.

[0034] The three electrodes were placed in neutral solutions with NO.sub.3.sup.−—N concentrations of 200 mg/L, 300 mg/L, and 500 mg/L, respectively, and a voltage of −1.5 V was applied for reaction for 24 hours. Subsequently, the concentration of the nitrate was measured after the reaction, and the removal rate of the nitrate and the selectivity of the nitrogen were calculated. The results are shown in FIG. 8. It can be seen from the results that the palladium-copper-loaded mesoporous silicon carbide-based catalyst prepared by the present invention can be used for the electrocatalytic denitrification reaction of nitrate-contaminated water with various initial concentrations.

[0035] The three electrodes were placed in solutions with a NO.sub.3.sup.−—N concentration of 100 mg/L and an initial pH of 3-11, respectively, and a voltage of −1.5 V was applied for reaction for 24 hours. Subsequently, the concentration of the nitrate was measured after the reaction, and the removal rate of the nitrate and the selectivity of the nitrogen were calculated. The results are shown in FIG. 9. It can be seen from the results that the palladium-copper-loaded mesoporous silicon carbide-based catalyst prepared by the present invention can be used for the electrocatalytic denitrification reaction of nitrate-contaminated water with various initial pH.

[0036] Embodiment 2, a preparation method of a palladium-copper-loaded mesoporous silicon carbide-based catalyst, which includes the steps as follows.

[0037] (1) 2 g of surfactant P123, 63.95 mL of deionized water and 10 mL of hydrochloric acid (12 M) were taken and put into a beaker, stirred until completely dissolved, and 4.25 g of tetraethyl orthosilicate was subsequently added dropwise to the beaker. A mechanical stirring was performed in a 40° C. water bath for 24 hours, and then the solution in the beaker was poured into a stainless-steel autoclave. Subsequently, the stainless-steel autoclave was placed in a 130° C. oven for static crystallization for 72 hours, followed by being subjected to cooling, filtering, drying and then calcining in a 550° C. muffle furnace for 6 hours to obtain mesoporous silica.

[0038] (2) 5 g of the mesoporous silica was taken and added to a 10 wt % xylene solution of polycarbosilane containing 6 g of the polycarbosilane, mixed and stirred until the xylene was completely volatilized, and then placed in a 80° C. oven for drying for 12 hours. After drying, the dried powder was placed in a tube furnace and calcined in a nitrogen atmosphere. In the tube furnace, the temperature was first raised to 350° C. at a rate of 2° C./min and kept for 5 hours, then raised to 700° C. at a rate of 0.5° C./min, and then raised to 1400° C. at a rate of 2° C./min and kept for 2 hours, and finally the dried powder was naturally cooled to room temperature under nitrogen protection. The cooled powder was taken and added to an excess of 4 wt % HF aqueous solution, stirred at room temperature for 24 hours, and then subjected to repeated washing, filtering, and drying to obtain mesoporous silicon carbide. The drying condition was 80° C. and the drying time was 12 hours.

[0039] (3) PdCl.sub.2 and Cu(NO.sub.3).sub.2.3H.sub.2O were mixed to obtain a copper-palladium precursor mixed solution. In the copper-palladium precursor mixed solution, a mass concentration of the palladium is 1 g/L; a mass concentration of the copper is 0.5 g/L.

[0040] (4) 1 g of the mesoporous silicon carbide was taken and added to 10 mL of the copper-palladium precursor mixed solution, mixed and stirred until the solvent was completely volatilized, dried in a 80° C. oven for 12 hours, and then placed in a tube furnace. The temperature was raised to 400° C. at a rate of 1° C./min for calcination in a nitrogen atmosphere for 3 hours and reduction in a hydrogen atmosphere for 1 hour to obtain a mesoporous silicon carbide-based catalyst loaded with palladium (1%) and copper (0.5%). The surface morphology of the mesoporous silicon carbide-based catalyst loaded with palladium and copper is shown in FIG. 2 and FIG. 5.

[0041] 4 mg of the mesoporous silicon carbide-based catalyst loaded with palladium (1%) and copper (0.5%) was taken and coated on a nickel foam to make a working electrode, a platinum electrode was used as a counter electrode, and a saturated calomel electrode was used as a reference electrode. The three electrodes were placed in a neutral solution with a volume of 20 mL and a NO.sub.3.sup.−—N concentration of 100 mg/L, and a voltage of −1.5 V was applied for reaction for 24 hours. Subsequently, the concentration of the nitrate was measured after the reaction, and the removal rate of the nitrate n and the selectivity of the nitrogen were calculated. The results are shown in FIG. 7.

[0042] Embodiment 3, a preparation method of a palladium-copper-loaded mesoporous silicon carbide-based catalyst, which includes the steps as follows.

[0043] (1) 2 g of surfactant P123, 63.95 mL of deionized water and 10 mL of hydrochloric acid (12 M) were taken and put into a beaker, stirred until completely dissolved, and 4.25 g of tetraethyl orthosilicate (TEOS) was subsequently added dropwise to the beaker. A mechanical stirring is performed in a 40° C. water bath for 24 hours, and then the solution in the beaker was poured into a stainless-steel autoclave. Subsequently, the stainless-steel autoclave was placed in a 130° C. oven for static crystallization for 72, followed by being subjected to cooling, filtering, drying and calcining in a 550° C. muffle furnace for 6 hours to obtain mesoporous silica.

[0044] (2) 5 g of the mesoporous silica was taken and added to a 10 wt % xylene solution of polycarbosilane containing 6 g of the polycarbosilane, mixed and stirred until the xylene was completely volatilized, and then placed in a 80° C. oven for drying for 12 hours. After drying, the dried powder was placed in a tube furnace and calcined in a nitrogen atmosphere. In the tube furnace, the temperature was first raised to 350° C. at a rate of 2° C./min and kept for 5 hours, then raised to 700° C. at a rate of 0.5° C./min, and then raised to 1400° C. at a rate of 2° C./min and kept for 2 hours, and finally the dried powder was naturally cooled to room temperature under nitrogen protection. The cooled powder was taken and added to an excess of 4 wt % HF aqueous solution, stirred at room temperature for 24 hours, and then subjected to repeated washing, filtering, and drying to obtain mesoporous silicon carbide. The drying condition was 80° C. and the drying time was 12 hours.

[0045] (3) PdCl.sub.2 and Cu(NO.sub.3).sub.2.3H.sub.2O were mixed to obtain a copper-palladium precursor mixed solution. In the copper-palladium precursor mixed solution, a mass concentration of the palladium is 5 g/L; a mass concentration of the copper is 2.5 g/L.

[0046] (4) 1 g of the mesoporous silicon carbide was taken and added to 10 mL of the copper-palladium precursor mixed solution, mixed and stirred until the solvent was completely volatilized, dried in an 80° C. oven for 12 hours, and then placed in a tube furnace. The temperature was raised to 400° C. at a rate of 1° C./min for calcination in a nitrogen atmosphere for 3 hours and reduction in a hydrogen atmosphere for 1 hour to obtain a mesoporous silicon carbide-based catalyst loaded with palladium (5%) and copper (2.5%). The surface morphology of the mesoporous silicon carbide-based catalyst loaded with palladium and copper is shown in FIG. 3 and FIG. 6.

[0047] 4 mg of the mesoporous silicon carbide-based catalyst loaded with palladium (5%) and copper (2.5%) was taken and coated on a nickel foam to make a working electrode, a platinum electrode was used as a counter electrode, and a saturated calomel electrode was used as a reference electrode. The three electrodes were placed in a neutral solution with a volume of 20 mL and a NO.sub.3.sup.−—N concentration of 100 mg/L, and a voltage of −1.5 V was applied for reaction for 24 hours. Subsequently, the concentration of the nitrate nitrogen was measured after the reaction, and the removal rate of the nitrate and the selectivity of the nitrogen were calculated. The results are shown in FIG. 7.

[0048] Prior art comparative example, a nitrogen-doped mesoporous carbon-based catalyst loaded with palladium and copper was prepared and applied to electrocatalytic removal of nitrate in water body. Specifically, 4 mg of catalyst was coated on a nickel foam to make a working electrode, a platinum electrode was used as a counter electrode, and a saturated calomel electrode was used as a reference electrode. The three electrodes were placed in a neutral solution with a volume of 20 mL and a NO.sub.3.sup.−—N concentration of 100 mg/L, and a voltage of −1.5 V was applied for reaction for 24 hours. Subsequently, the concentration of the nitrate was measured after the reaction, and the removal rate of the nitrate and the selectivity of the nitrogen were calculated. The results are shown in FIG. 7.

[0049] It can be seen from FIG. 7 that the palladium-copper-loaded mesoporous silicon carbide-based catalyst prepared by the present invention has a higher catalytic activity at a low loading amount. Compared with the existing palladium-copper catalytic system, the catalyst of the present invention has higher removal rate of the nitrate in water body and significantly improved selectivity of the nitrogen. Especially, the catalyst with a palladium loading amount of 0.1% and a copper loading amount of 0.05% in embodiment 1 achieves the nitrate nitrogen removal rate of 94.5% and the product nitrogen selectivity of up to 91.2%.

[0050] Those skilled in the art should understand that the present invention can be implemented in many other specific forms without departing from the spirit or scope of the present invention. Although the embodiments of the present invention have been described, it should be understood that the present invention shall not be limited to such embodiments. Those skilled in the art can make changes and modifications within the spirit and scope of the present invention as defined by the appended claims.