A CuZnCeO x Preparation of nanorod catalyst and its application in the photocatalytic and thermocatalytic reduction of CO2

Abstract

The present invention discloses the preparation of a CuZnCeO x nanorod catalyst and its application in the photo-thermal synergistic catalysis of CO2 reduction. The Cu / ZnO@CeO2 catalyst with a nanorod structure is synthesized by a hydrothermal technique, and the loading amount of the active metal Cu is 5-15%. This catalyst exhibits high activity and stability in the photo-thermal synergistic catalysis of CO2, and there is no obvious deactivation after continuous reaction for 50 h. The morphological effect of the catalyst and the strong interaction between the transition metal and the support greatly enhance the ability of the catalyst to activate inert CO2 and inhibit the serious problems of active metal sintering and carbon deposition during the reaction process. The preparation of the catalyst of the present invention has the advantages of simple process, low process energy consumption, low cost without noble metals, etc., which is in line with the development trend of green chemical industry; and it shows high application potential in the field of photo-thermal synergistic catalytic conversion of greenhouse gas CO2, promoting the high-value utilization of CO2.

Description

Technical Field

[0001] The present invention belongs to the technical fields of greenhouse gas treatment and catalytic chemistry, involving the intersection and integration of environmental protection, nanomaterials, and catalytic chemistry. Specifically, it relates to the preparation of a CuZnCeO x nanorod catalyst and its application in the photo-thermal synergistic catalytic reduction of CO2. Background Art

[0002] Carbon dioxide is the most important greenhouse gas today. Large-scale CO2 emissions can lead to a series of serious environmental problems such as global warming and ocean acidification. Currently, countries around the world are facing severe CO2 emission reduction pressure. At the same time, CO2 is also a cheap and abundant C1 resource. Therefore, it is of great significance to convert it into high-value chemicals and liquid fuels by means of chemical catalytic technology. This can not only reduce greenhouse gas emissions but also realize the resource utilization of carbon dioxide. Among them, the reforming of methane and carbon dioxide to syngas is a relatively promising route in the high-value conversion of CO2. The theoretical value of H2 / CO in the obtained syngas is 1, which can be used to produce engine fuels such as gasoline, kerosene, and diesel through Fischer-Tropsch synthesis, and industrial chemicals such as ethers and ketones can also be obtained. However, methane is the main component of the fossil resource natural gas, which does not meet the requirements of the green and sustainable development strategy. Therefore, using renewable resources such as biomass ethanol for dry reforming with CO2 to produce syngas is a feasible strategy for realizing CO2 emission reduction and sustainable utilization of carbon resources, and has become one of the hotspots in current green chemistry research; Biomass fermentation to produce ethanol is already a relatively mature process in the biomass conversion process, and ethanol has the characteristics of being renewable and environmentally friendly. Although recent research on the ethanol dry reforming reaction at home and abroad has made certain progress, mainly using the traditional thermal catalytic method, there are problems such as relatively high reaction temperature and serious catalyst sintering and carbon deposition; Therefore, how to efficiently catalyze the reforming reaction of ethanol and CO2 is still one of the extremely challenging hot topics in the research of carbon dioxide catalytic conversion.

[0003] Thermal catalysis and photocatalysis are currently commonly used catalytic technologies, but both have deficiencies. Thermal catalysis has high energy consumption and affects the stability and selectivity of products, while the initial energy of incident light in photocatalysis cannot effectively initiate some target reactions. Therefore, constructing a photocatalysis and thermal catalysis coupling system (photo-thermal synergy) can effectively solve the technical deficiencies of single catalytic technologies and open up a widely applicable new catalytic approach.

[0004] There are few literature reports on the research of special-shaped composite metal catalysts for ethanol dry reforming at home and abroad, and there are no patent reports on the application of copper-based catalysts with specific morphological structures in the field of photo-thermal synergistic catalytic reduction of CO2. Summary of the Invention

[0005] To solve the above bottleneck problems in the prior art, the object of the present invention is to synthesize a Cu / ZnO nanorod catalyst with uniform morphology by a hydrothermal technique, and a strong interaction between Cu and Zn is formed by a CuZn solid solution and a specific morphology structure; a Cu / ZnO@CeO2 composite metal catalyst with a nanorod structure is synthesized by a precipitation method. The selective deposition of the promoter Ce on the surface of the Cu / ZnO nanorods is regulated to form an interfacial structure with strong interaction; through the optimized design of the interfacial structure, the electronic structure of the Cu active site, as well as the size and dispersion state of the Cu particles are regulated, the sintering of the active component Cu during the reaction is inhibited, and the stability of the catalyst is improved; the addition of the promoter Ce further enhances the redox ability of the catalyst and improves the ability of the catalyst to activate CO2.

[0006] To achieve the above object of the invention, the present invention provides a preparation of a CuZnCeO x nanorod catalyst, and the preparation method comprises the following steps:

[0007] ① Preparation of Cu / ZnO nanorods

[0008] Under the condition of 25 - 40 °C, a soluble Cu salt and triethylenetetramine (TETA) are dissolved in deionized water to form solution A. A soluble Zn salt is dissolved in deionized water to form solution B. After solution B is poured into solution A, ammonia water is added dropwise until the pH = 8 - 10. The mixture is transferred to a hydrothermal reaction kettle and reacted at 120 - 160 °C for 20 - 32 h. After cooling to room temperature, the precipitate obtained by suction filtration is calcined to obtain Cu / ZnO nanorods.

[0009] Further, in step ①, the soluble Cu salt is one of Cu(NO3)2·3H2O and CuCl2; the soluble Zn salt is one of Zn(CH3COO)2·2H2O and ZnSO4·7H2O.

[0010] Further, 0.4 - 0.6 g of Cu(NO3)2·3H2O is dissolved in 280 - 300 mL of deionized water, and then 5 - 8 drops of triethylenetetramine (TETA) are added dropwise to form solution A. At the same time, 3 - 5 g of Zn(CH3COO)2·2H2O is dissolved in 80 - 100 mL of deionized water to form solution B. After each is stirred for 0.5 - 1.5 h, solution B is poured into solution A; after continuous stirring for 1 - 2 h, NH3·H2O is added dropwise to adjust the pH = 8 - 10; after continuing to stir for 1 - 2 h, the mixed solution is transferred to a hydrothermal reaction kettle and maintained at 120 - 160 °C for 20 - 32 h. After cooling to room temperature, suction filtration is carried out, and the precipitate is washed several times with deionized water and ethanol, and then dried overnight at 60 - 90 °C; then it is calcined in a muffle furnace at 400 - 600 °C for 3 - 5 h. The loading amount of the active metal Cu is 5 - 15%.

[0011] ② Preparation of Cu / ZnO@CeO2

[0012] Under the condition of a water bath at 60 - 80 °C, the Cu / ZnO nanorods prepared in step ① and the soluble Ce salt are dissolved in ethanol. After adding hexamethylenetetramine, the reaction is carried out for 6 - 8 h. The obtained precipitate is washed, dried, and then calcined to obtain the Cu / ZnO@CeO2 catalyst.

[0013] Furthermore, the soluble Ce salt in step ② is one of CeCl3·7H2O and Ce(NO3)3·6H2O. The calcination process in step ② is carried out in a muffle furnace at 400 - 700 °C for 3 - 5 h.

[0014] Furthermore, under the condition of a water bath at 60 - 80 °C, 1 - 1.5 g of Cu / ZnO and 1 - 1.5 g of CeCl3·7H2O are dissolved in 200 mL of ethanol. Then 18 - 22 g of hexamethylenetetramine is added, and the mixture is stirred for 6 - 8 h. After cooling to room temperature, filtration is carried out, and the precipitate is washed several times with ethanol and water, and then dried overnight at 60 - 90 °C; then it is calcined in a muffle furnace at 400 - 600 °C for 3 - 5 h.

[0015] A CuZnCeO x nanorod catalyst prepared by the above preparation method, the catalyst has a Cu / ZnO@CeO2 nanorod structure, the active metal Cu and ZnO form a uniform solid solution, and the surface is uniformly coated with CeO2. The loading amount of the active metal Cu is 5 - 15%.

[0016] A CuZnCeO as described above x Application of the nanorod catalyst in the photo-thermal synergistic catalytic reduction of CO2 to high-value syngas reaction. Using a traditional fixed-bed reactor, the catalyst is added into a quartz reaction tube; the reaction temperature is 300 - 550 °C, the reaction pressure is atmospheric pressure, and the power of the xenon lamp light source is 50 - 300 W. 0.05 - 0.3 g of the catalyst is added into the quartz reaction tube; the reactant is a C2H5OH / CO2 / N2 mixed gas with a molar ratio of 1 / 1 / 3, and the reaction space velocity is 30000 - 85000 mLg -1 h -1 。

[0017] Furthermore, the reaction is carried out in a fixed-bed reactor. 0.05 - 0.1 g of the sifted (40 - 60 mesh) catalyst is placed into a quartz reaction tube with an inner diameter of 8 mm. Before the reaction, the catalyst is on-line reduced in 5 vol% H2 / N2 (flow rate 30 - 60 mL / min) at 400 - 600 °C for 0.5 - 2 h. After purging with nitrogen until the temperature drops to the reaction temperature, under the illumination of a 50 - 300 W xenon lamp, the dry reforming reaction of ethanol is carried out at 350 - 550 °C. The inert gas nitrogen is used as the diluent gas, and the reactants are a C2H5OH / CO2 / N2 mixed gas with a molar ratio of 1 / 1 / 3. The reaction space velocity is 30000 - 80000 mLg -1 h -1 。

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] The catalyst prepared by the present invention has excellent performance. This catalyst exhibits excellent catalytic activity and stability in the photo-thermal synergistic CO2 reduction reaction. The strong interaction and interfacial structure between the active metal Cu and the promoter Ce are beneficial to inhibiting the sintering of the active component Cu during the reaction, while enhancing the activation ability of CO2, providing active oxygen species, realizing the dynamic elimination of carbon deposition, and avoiding the formation of carbon deposition. Description of the Drawings

[0020] Figure 1 Field emission scanning electron microscope photograph of the CuZnCeO x nanorod catalyst prepared in Example 1;

[0021] Figure 2 Catalytic reaction activity test chart of Application Example 1;

[0022] Figure 3 Catalytic reaction stability test chart of Application Example 4. Detailed Embodiments

[0023] The following further illustrates the present invention with specific embodiments, but does not limit the present invention in any way. To avoid repetition, in the following embodiments, the raw materials are all commercially available products without special instructions, and the methods used are all conventional methods without special instructions.

[0024] Example 1

[0025] Preparation of a CuZnCeO x nanorod catalyst. The preparation method includes the following steps:

[0026] ① Preparation of Cu / ZnO nanorods

[0027] At room temperature, 0.4 g of Cu(NO3)2·3H2O was dissolved in 300 mL of deionized water, and then 5 drops of triethylenetetramine (TETA) were added dropwise to form solution A. At the same time, 3 g of Zn(CH3COO)2·2H2O was dissolved in 100 mL of deionized water to form solution B. After stirring each for 30 min, solution B was poured into solution A. After continuous stirring for 1 h, NH3·H2O was added dropwise to adjust the pH to 10. Stirring was continued for 1 h. Then the mixed solution was transferred to a reaction kettle and maintained at 130 °C for 24 h. After cooling to room temperature, suction filtration was carried out, and it was washed several times with deionized water and ethanol, and then dried overnight at 60 °C. Then it was calcined in a muffle furnace at 400 °C for 4 h.

[0028] ② Preparation of Cu / ZnO@CeO2

[0029] Under the condition of a water bath at 70 °C, 1 g of Cu / ZnO and 1.5 g of CeCl3·7H2O were dissolved in 200 mL of ethanol, and then 20 g of hexamethylenetetramine was added, and it was stirred for 7 h. After cooling to room temperature, suction filtration was carried out, and it was washed several times with ethanol and water. Then it was dried overnight at 60 °C. Then it was calcined in a muffle furnace at 550 °C for 4 h, and the obtained catalyst was named Cu / ZnO@CeO2. The field emission scanning electron microscope photograph of the prepared Cu / ZnO@CeO2 catalyst is as Figure 1 shown. The catalyst has a uniform nanorod-like morphology with a diameter of 500 - 900 nm; the promoter cerium oxide is uniformly dispersed on the surface, and the cerium oxide particle size is 15 - 25 nm.

[0030] Comparative Example 1

[0031] A commercial ZnO support was purchased and the active metal copper Cu was supported by the same precipitation method as in Example 1, and the obtained catalyst was named Cu / ZnO@CeO2-C. The loading amount of the active metal Cu was 5 - 15%.

[0032] Application Example 1

[0033] 0.10 g of the Cu / ZnO@CeO2 catalyst prepared in Example 1 was added to a quartz reaction tube, with ethanol / carbon dioxide / nitrogen = 1 / 1 / 3 (molar ratio) and a space velocity of 34000 mLg -1 h -1 , and the reaction pressure was atmospheric pressure. The reaction was carried out at 500 °C under xenon lamp irradiation (power 50 W) (photo-thermal synergy) and without a light source (thermal catalysis). The reaction results are as Figure 2 shown. Under xenon lamp irradiation (photo-thermal synergy), the ethanol conversion rate on the Cu / ZnO@CeO2 catalyst was 90.3%; while without a light source (thermal catalysis), the ethanol conversion rate was only 71%, and more by-products were generated. It shows that under photo-thermal synergy catalysis, the Cu / ZnO@CeO2 nanorod catalyst exhibits more excellent catalytic activity.

[0034] Applied Comparative Example 1

[0035] 0.10 g of Cu / ZnO@CeO2 and Cu / ZnO@CeO2-C catalysts were respectively added to a quartz reaction tube to test the catalytic performance. Ethanol / carbon dioxide / nitrogen = 1 / 1 / 3 (molar ratio), and the space velocity was 34000 mLg -1 h -1 , and the reaction pressure was atmospheric pressure. The reaction was carried out at 500 °C under the irradiation of a xenon lamp (power 50 W). The reaction results are shown in Table 1. At 500 °C, ethanol / carbon dioxide / nitrogen = 1 / 1 / 3 (molar ratio), and the space velocity was 34000 mLg -1 h -1 , and under the condition of a xenon lamp power of 50 W, the ethanol conversion rate of the commercial Cu / ZnO@CeO2-C catalyst was only 68.2%, which was much lower than 90.3% of the Cu / ZnO@CeO2 catalyst. Moreover, the commercial Cu / ZnO@CeO2-C catalyst produced more by-product methane (5.7 mol%).

[0036] Table 1 Influence of preparation technology on the performance of Cu / ZnO@CeO2 catalyst

[0037]

[0038] Applied Example 2

[0039] 0.10 g of Cu / ZnO@CeO2 catalyst was added to a quartz reaction tube to test the catalytic performance. Ethanol / carbon dioxide / nitrogen = 1 / 1 / 3 (molar ratio), and the space velocity was 34000 mLg -1 h -1 , and the reaction pressure was atmospheric pressure. The reaction was carried out under the irradiation of a xenon lamp (power 50 W). The results are shown in Table 2. As the reaction temperature increased, the ethanol conversion rate gradually increased, which was consistent with the endothermic characteristics of the ethanol dry reforming reaction. The hydrogen selectivity increased, accompanied by a decrease in the carbon monoxide selectivity. The selectivity of by-product methane gradually decreased because the methane dry reforming reaction was favored at high reaction temperatures.

[0040] Table 2 Influence of reaction temperature on the performance of Cu / ZnO@CeO2 catalyst

[0041]

[0042] Applied Example 3

[0043] 0.10 g of the Cu / ZnO@CeO2 catalyst was added to a quartz reaction tube to test its catalytic performance. Ethanol / carbon dioxide / nitrogen = 1 / 1 / 3 (molar ratio), the reaction temperature was 500 °C, and the reaction pressure was atmospheric pressure. The reaction was carried out under the irradiation of a xenon lamp (power 50 W). The reaction results are shown in Table 3. As the reaction space velocity increased, the ethanol conversion rate over Cu / ZnO@CeO2 decreased, and the selectivity of the by-product methane increased. This was because the increase in space velocity led to a decrease in the contact time between the reactants and the catalytic active sites, resulting in a decrease in the activity of the catalyst.

[0044] Table 3 Effect of reaction space velocity on the performance of the Cu / ZnO@CeO2 catalyst

[0045]

[0046] Application Example 4

[0047] 0.10 g of the Cu / ZnO@CeO2 catalyst was added to a quartz reaction tube to test its catalytic performance. Ethanol / carbon dioxide / nitrogen = 1 / 1 / 3 (molar ratio), the reaction temperature was 500 °C, and the space velocity was 34000 mLg -1 h -1 , and the reaction pressure was atmospheric pressure. The reaction was carried out under the irradiation of a xenon lamp (power 50 W). The reaction results are as Figure 3 shown. After the Cu / ZnO@CeO2 nanorod composite catalyst reacted for 50 h, its reaction performance did not decrease significantly. During the continuous test process, the ethanol conversion rate remained at about 90%, and the selectivities of the target products hydrogen and carbon monoxide were maintained at about 60 mol% and 30 mol%, respectively. At the same time, the selectivities of the by-products methane, acetone, and acetaldehyde did not increase significantly and remained below 4 mol%. The results of the stability test proved that the catalyst exhibited excellent catalytic stability.

[0048] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A preparation method of a CuZnCeO x nanorod catalyst, characterized in that The preparation method includes the following steps: ① Preparation of Cu / ZnO nanorods Under the condition of 25 - 40 °C, dissolve soluble Cu salt and triethylenetetramine in deionized water to form solution A; Dissolve soluble Zn salt in deionized water to form solution B; pour solution B into solution A, then add ammonia water until pH = 8 - 10; transfer the mixture to a hydrothermal reaction kettle and react at 120 - 160 °C for 20 - 32 h; after cooling to room temperature, calcine the precipitate obtained by suction filtration to obtain Cu / ZnO nanorods; ② Preparation of Cu / ZnO@CeO2 Under the condition of a water bath at 60 - 80 °C, dissolve the Cu / ZnO nanorods prepared in step ① and soluble Ce salt in ethanol, add hexamethylenetetramine and react for 6 - 8 h; wash and dry the obtained precipitate, and then calcine it to obtain the Cu / ZnO@CeO2 catalyst.

2. The preparation method of the catalyst according to claim 1, wherein, The soluble Cu salt described in step ① is one of Cu(NO3)2·3H2O and CuCl2; the soluble Zn salt is one of Zn(CH3COO)2·2H2O and ZnSO4·7H2O.

3. The preparation method of the catalyst according to claim 1, characterized in that, The soluble Ce salt described in step ② is one of CeCl3·7H2O and Ce(NO3)3·6H2O.

4. The preparation method of the catalyst according to claim 1, characterized in that, The calcination process in step ② is carried out in a muffle furnace at 400 - 700 °C for 3 - 5 h.

5. A CuZnCeO nanorod catalyst prepared by the preparation method according to any one of claims 1-4, characterized in that, x The catalyst has a Cu / ZnO@CeO2 nanorod-like structure, the active metal Cu forms a uniform solid solution with ZnO, and the surface is uniformly coated with CeO2. ​ 6. Use of the CuZnCeO nanorod catalyst as described in claim 5 x in the photocatalytic and thermocatalytic reduction of CO2.

7. The application according to claim 6, wherein Using a fixed-bed reactor, add the catalyst into a quartz reaction tube; the reaction temperature is 300 - 550 °C, the reaction pressure is atmospheric pressure, and the power of the xenon lamp light source is 50 - 300 W.

8. The application according to claim 6, wherein Add 0.05 - 0.3 g of the said catalyst into a quartz reaction tube; the reactants are a mixed gas of C2H5OH / CO2 / N2 with a molar ratio of 1 / 1 / 3, and the reaction space velocity is 30000 - 85000 mLg -1 h -1 。

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