Metal-doped zinc oxide quantum dot catalysts, their preparation methods and applications in carbon dioxide to syngas production methods

Abstract

This invention relates to the field of electrocatalytic CO2 reduction technology, and discloses a metal-doped zinc oxide quantum dot catalyst, its preparation method, and its application. Based on the total weight of the catalyst, the metal-doped zinc oxide quantum dot catalyst contains 95-100 wt% zinc oxide and 1-5 wt% doped metal; and the zinc oxide and doped metal exist in the form of a solid solution. The catalyst of this invention can be prepared by the following method: (1) dissolving zinc salt and metal salt in an alcohol solvent to obtain mixed solution I; (2) reacting mixed solution I with an alcohol solution of alkali to obtain mixed solution II; (3) mixing mixed solution II with a solvent and treating it. The metal-doped zinc oxide quantum dot catalyst used in the electrochemical reduction reaction of carbon dioxide to prepare carbon monoxide not only has higher catalytic activity and CO selectivity, but also allows for the control of the syngas ratio within a wide range, which is beneficial for the synthesis of downstream products of syngas.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic CO2 reduction technology, specifically to a metal-doped zinc oxide quantum dot catalyst, its preparation method, and its application in the production of syngas from carbon dioxide. Background Technology

[0002] In recent years, to alleviate the global problem caused by excessive CO2 emissions, the efficient conversion of CO2 into usable fuels and other value-added chemicals has become a research hotspot. This can not only reduce CO2 emissions but also, to some extent, address the energy shortage problem. Catalysts are the core of electrocatalytic reactions, and designing and preparing electrocatalysts with high activity, high selectivity, and long lifetime is the primary task in the field of CO2 electroconversion research. Many studies in recent years have focused on designing highly efficient electrocatalysts for converting CO2 to CO. Au and Ag are good catalysts for the electrocatalytic reduction of CO2 to CO. By designing different Au and Ag nanostructures, their activity in the hydrogen evolution reaction can be suppressed, thereby improving the selectivity for CO products. However, Au and Ag catalysts are precious metal catalysts, with limited reserves and high prices, restricting their large-scale practical application. Therefore, researching inexpensive and efficient non-precious metal catalysts is one of the key scientific problems in achieving low-cost electrocatalytic conversion of CO2 to CO.

[0003] CN112647099A discloses an electrodeposition method for preparing transition metal nanocatalysts. First, a metastable mixed electrodeposition solution is formed by adding a sparingly soluble transition metal salt (i.e., precursor), oxide, and stabilizer polyvinylpyrrolidone (PVP) to a K₂SO₄ or KHCO₃ solution, along with ethanol. Then, a pure copper sheet or carbon material is immersed in the electrodeposition solution, and electrodeposition is performed under constant voltage. This invention utilizes the electric field generated during electrodeposition to adsorb the sparingly soluble metal salt and oxide to form metal nanostructures, suitable for transition metal elements such as Cu, Ag, Au, Zn, and Sn. The catalyst prepared by this invention exhibits excellent performance and shows promising application prospects in electrocatalysis, photocatalytic reduction of CO₂, and oxygen reduction.

[0004] CN104959135A discloses a nano-zinc catalyst and a method for efficiently catalyzing the reduction of CO from CO2 based on the nano-zinc catalyst. The nano-zinc catalyst is grown on a zinc substrate and is a nanosheet array structure with nanoparticles grown on the surface of the nanosheets. In an electrolytic cell divided into an anode and cathode compartments by a proton exchange membrane, the aforementioned nano-zinc catalyst electrode is used as the working electrode (cathode), a platinum sheet as the auxiliary electrode (anode), and a saturated calomel electrode as the reference electrode. Electrolyte solutions are placed in both the anode and cathode compartments. CO2 is introduced into the cathode compartment until saturation, and then CO2 is reduced at a constant potential under continuous CO2 introduction. The potential control range during the constant potential reduction process is -1.4 to -1.8 V.

[0005] Compared with bulk zinc electrodes, the obtained nanostructured zinc electrodes generally exhibit higher catalytic activity and CO selectivity, but neither can achieve efficient catalytic conversion of CO2 into syngas, while simultaneously enabling the control of the proportion of syngas over a wide range to facilitate the synthesis of downstream syngas products. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of existing technologies in achieving efficient catalytic conversion of CO2 into syngas and in controlling the proportion of syngas over a wide range, and to provide a metal-doped zinc oxide quantum dot catalyst, its preparation method, and its application in the production of syngas from carbon dioxide.

[0007] To achieve the above objectives, the first aspect of the present invention provides a metal-doped zinc oxide quantum dot catalyst, wherein, based on the total weight of the metal-doped zinc oxide quantum dot catalyst, the metal-doped zinc oxide quantum dot catalyst contains 95-100 wt% zinc oxide and 1-5 wt% doping metal; and the zinc oxide and the doping metal exist in the form of a solid solution.

[0008] A second aspect of the present invention provides a method for preparing a metal-doped zinc oxide quantum dot catalyst, wherein the method includes:

[0009] (1) Dissolve zinc salt and metal salt in alcohol solvent to obtain mixed solution I;

[0010] (2) The mixed solution I is reacted with an alcoholic solution of alkali to obtain mixed solution II;

[0011] (3) The mixed solution II is mixed with a solvent and processed to obtain the metal-doped zinc oxide quantum dot catalyst.

[0012] A third aspect of the present invention provides a metal-doped zinc oxide quantum dot catalyst prepared by the preparation method of the second aspect of the present invention.

[0013] The fourth aspect of this invention provides the application of a metal-doped zinc oxide quantum dot catalyst in the electrochemical reduction reaction of carbon dioxide.

[0014] The fifth aspect of the present invention provides a method for producing syngas from carbon dioxide, wherein the method comprises: performing an electrochemical reduction reaction of carbon dioxide and water in the presence of a metal-doped zinc oxide quantum dot catalyst provided by the present invention to obtain syngas.

[0015] Through the above technical solution, in the metal-doped zinc oxide quantum dot catalyst provided by the present invention, the oxidation state ionic radius of the dopant element is similar to that of Zn. 2+ Different radii of the ions cause distortion of the zinc oxide lattice during solid solution formation; moreover, because different dopants have different radii of oxidation state ions, the degree of lattice distortion caused by doping zinc oxide also varies. The lattice distortion of zinc oxide caused by dopants, and the different degrees of distortion caused by different dopants, can be observed from the XRD patterns of the products (e.g., ...). Figure 1 This is shown in the diagram. From Figure 1 It can be seen that, based on the ratio of the oxidation state ionic radius of the doped element to that of Zn 2+ Whether the radius is large or small, the distortion of the zinc oxide lattice causes the diffraction peaks of the crystal plane to shift towards larger or smaller angles. Furthermore, depending on the doping element, the angle of shift of the diffraction peaks corresponding to the same crystal plane is also different.

[0016] This invention relates to a metal-doped zinc oxide quantum dot catalyst, wherein the electronegativity of the oxidation state of the dopant element is similar to that of Zn. 2+ The electronegativity of the dopant elements differs, and in the electrocatalytic CO2 reduction process, this difference in electronegativity causes electron transfer between the dopant element and zinc. Since carbon dioxide activation is an electron-dependent process, this electron transfer phenomenon can further promote carbon dioxide activation, thereby enhancing catalytic activity. Furthermore, the different oxidation states of the dopant elements have different electronegativity; therefore, when doping zinc oxide, the degree of electron transfer between different dopant elements and zinc also varies, resulting in different degrees of promotion of carbon dioxide activation. The oxidation state of the dopant element and Zn... 2+ The effect of electronegativity differences between the two on the selectivity of CO production from electrocatalytic CO2 reduction and on the control of syngas ratios can be found in [reference needed]. Figure 3 , 4 5. From Figure 3 and 4It can be seen that, under the same reaction conditions, when using undoped ZnO quantum dots for electrocatalytic CO2 reduction to CO, the maximum CO Faradaic efficiency obtained is 78.4%, and the syngas ratio can be adjusted between 0.9 and 3.7 by controlling the potential (between -0.7 and -1.4 V vs. RHE). When using Cu or Fe doped ZnO quantum dots, the selectivity of the doped ZnO quantum dot catalyst for CO decreases significantly compared to ZnO quantum dots, and the maximum CO Faradaic efficiency is reduced to 68.4% or 64.9%, and the syngas adjustment range is also narrowed to 0.6-2.2 or 0.8-1.8. However, when using Co or Ni doped ZnO quantum dots, the selectivity of the doped ZnO quantum dot catalyst for CO is enhanced compared to ZnO quantum dots, and the maximum CO Faradaic efficiency is enhanced to 89.9% or 82.9%, and the syngas adjustment range is expanded to 1.3-9 or 1.2-4.8. Therefore, the metal-doped zinc oxide quantum dot catalyst provided by this invention not only effectively promotes the activation of carbon dioxide and achieves high catalytic reducibility and selectivity, but also enables the control of the proportion of syngas within a wide range, which is beneficial to the synthesis of downstream products of syngas.

[0017] In addition, the synthesis method used in this invention is simple, easy to operate and control, and does not use toxic reaction raw materials, making it an environmentally friendly green synthesis process. Attached Figure Description

[0018] Figure 1 These are XRD patterns of zinc oxide quantum dots and zinc oxide quantum dot catalysts doped with different transition metals;

[0019] Figure 2 This is a high-magnification TEM image of the zinc oxide quantum dot catalyst obtained in Comparative Example 1;

[0020] Figure 3 The Faraday efficiency and syngas ratio of the zinc oxide quantum dot catalyst obtained in Comparative Example 1 for CO production are shown.

[0021] Figure 4 The Faraday efficiency and syngas ratio of the doped zinc oxide quantum dot catalysts obtained in Examples 1-4 for CO production are as follows: a: Cu-ZnO, b: Ni-ZnO, c: Fe-ZnO, d: Co-ZnO;

[0022] Figure 5 This is a comparison chart of the Faraday efficiencies of the zinc oxide quantum dots obtained in Comparative Example 1 and the different transition metal doped catalysts obtained in Examples 1-4 for CO production. Detailed Implementation

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] The first aspect of the present invention provides a metal-doped zinc oxide quantum dot catalyst, wherein, based on the total weight of the metal-doped zinc oxide quantum dot catalyst, the metal-doped zinc oxide quantum dot catalyst contains 95-100 wt% zinc oxide and 1-5 wt% doping metal; and the zinc oxide and the doping metal exist in the form of a solid solution.

[0026] Non-precious metal-based catalysts are an important research system for CO2 electroconversion. They possess tunability and designability; by precisely controlling the size, composition, morphology, and structure of nanocatalysts, and supplementing this with instrumental characterization, the catalytic mechanism and reaction pathways of different products can be studied, enabling efficient, highly selective, and tunable CO2 electroconversion. Zn, as an abundant metal on Earth, can also reduce CO2 to CO, but its activity and CO selectivity are relatively low compared to Au and Ag catalysts. To overcome these limitations, the first aspect of this invention provides a metal-doped zinc oxide quantum dot catalyst.

[0027] In the metal-doped zinc oxide quantum dot catalyst of this invention, the electronegativity of the oxidation state of the dopant element is similar to that of Zn. 2+ The electronegativity of the dopant elements differs, and in the electrocatalytic CO2 reduction process, this difference in electronegativity causes electron transfer between the dopant element and zinc. Since carbon dioxide activation is an electron-dependent process, this electron transfer phenomenon can further promote carbon dioxide activation, thereby enhancing catalytic activity. Furthermore, the different oxidation states of the dopant elements have different electronegativity; therefore, when doping zinc oxide, the degree of electron transfer between different dopant elements and zinc also varies, resulting in different degrees of promotion of carbon dioxide activation. The oxidation state of the dopant element and Zn... 2+ The effect of electronegativity differences between the two on the selectivity of CO production from electrocatalytic CO2 reduction and on the control of syngas ratios can be found in [reference needed]. Figure 3 , 4 5.

[0028] In some embodiments of the present invention, the doping elements are Cu, Fe, Co or Ni respectively. Among them, the electronegativity order of the doping elements and Zn is Zn < Fe < Cu ≈ Co < Ni. Therefore, Zn all shows a tendency to gain electrons. In addition, if the electronegativity difference between elements is too small, the electron transfer ability between elements will not be strong enough, and the promotion effect on the electron gain activation of CO2 is not obvious; if the electronegativity difference between elements is too large, Zn will be too negatively charged, which is not conducive to the adsorption of CO2- intermediates. The influence of the doped metal elements on the zinc oxide quantum dots is also related to the adsorption ability of the doped metal to hydrogen and CO2 in addition to the electronegativity.

[0029] In the present invention, the method for preparing the metal-doped zinc oxide quantum dot catalyst can adopt the preparation method provided in the second aspect of the present invention.

[0030] For the metal-doped zinc oxide quantum dot catalyst according to the present invention, preferably, the crystal structure of the metal-doped zinc oxide quantum dot catalyst satisfies the following relationship: 0° < |A 110 -B 110 | ≤ 1.8°, where A 110 and B 110 respectively represent the 2θ values of the diffraction peaks characterizing the (110) plane of ZnO in the XRD spectra of the metal-doped zinc oxide quantum dot catalyst and the XRD spectrum of zinc oxide obtained under the same XRD measurement conditions.

[0031] 0° < |A 002 -B 002 | ≤ 1.8°, where A 002 and B 002 respectively represent the 2θ values of the diffraction peaks characterizing the (002) plane of ZnO in the XRD spectra of the metal-doped zinc oxide quantum dot catalyst and the XRD spectrum of zinc oxide obtained under the same XRD measurement conditions.

[0032] In some embodiments of the invention, preferably, the crystal structure of the copper-doped zinc oxide quantum dot catalyst satisfies the following relationships: A 110 -B 110 = 0.76°, A 002 -B 002 = 0.9°.

[0033] Preferably, the crystal structure of the iron-doped zinc oxide quantum dot catalyst satisfies the following relationships: A 110 -B 110 = 1.8°, A 002 -B 002 = 1.73°.

[0034] Preferably, the crystal structure of the cobalt-doped zinc oxide quantum dot catalyst satisfies the following relationship: A 110 -B 110 = -0.74°, A 002 -B 002 = -0.54°.

[0035] Preferably, the crystal structure of the nickel-doped zinc oxide quantum dot catalyst satisfies the following relationship: A 110 -B 110 = -1.44°, A 002 -B 002 = -1.24°.

[0036] According to the present invention, in order to distort the lattice of zinc oxide in the metal-doped zinc oxide quantum dot catalyst and to generate electron transfer between the dopant element and the zinc element, so as to ensure that the electrocatalytic CO2 reduction process achieves efficient, highly selective and controllable CO2 conversion to CO, preferably, in the metal-doped zinc oxide quantum dot catalyst, the dopant metal is selected from transition metals, and more preferably selected from one or more of copper, iron, cobalt and nickel.

[0037] In some embodiments of the invention, preferably, the doped metal in the metal-doped zinc oxide quantum dot catalyst is copper, iron, cobalt, or nickel.

[0038] According to the present invention, the average particle size of the metal-doped zinc oxide quantum dot catalyst is 3-15 nm. This can be determined using a laser particle size analyzer.

[0039] In some embodiments of the invention, preferably, the average particle size of the metal-doped zinc oxide quantum dot catalyst is 10 nm.

[0040] In this invention, the composition and structure of the metal-doped zinc oxide quantum dot catalyst can be determined by XRD and HRTEM testing methods, or by the amount of each material fed during the preparation process.

[0041] A second aspect of the present invention provides a method for preparing a metal-doped zinc oxide quantum dot catalyst, wherein the method includes:

[0042] (1) Dissolve zinc salt and metal salt in alcohol solvent to obtain mixed solution I;

[0043] (2) The mixed solution is reacted with an alcoholic solution of alkali to obtain mixed solution II;

[0044] (3) The mixed solution II is mixed with a solvent and processed to obtain the metal-doped zinc oxide quantum dot catalyst.

[0045] This invention prepares the metal-doped zinc oxide quantum dot catalyst using a solvothermal method. The electronegativity of the oxidation state of the doped metal is similar to that of Zn. 2+ The different electronegativity of the dopant elements leads to electron transfer between them and zinc. Carbon dioxide activation is an electron-dependent process, and this electron transfer can further promote carbon dioxide activation, thereby enhancing catalytic activity. Furthermore, the different electronegativity of the oxidation states of different dopant elements results in varying degrees of electron transfer between them and zinc when doping zinc oxide, thus affecting their promotion of carbon dioxide activation. The oxidation state of the dopant element and Zn... 2+ The effect of electronegativity differences between the two on the selectivity of CO production from electrocatalytic CO2 reduction and on the control of syngas ratios can be found in [reference needed]. Figure 3 , 4 5.

[0046] According to the present invention, in order to distort the lattice of zinc oxide in the metal-doped zinc oxide quantum dot catalyst and to generate electron transfer between the dopant element and the zinc element, so as to ensure that the electrocatalytic CO2 reduction process achieves efficient, highly selective and controllable CO2 conversion to CO, preferably, in step (1), the mass ratio of zinc salt to metal salt is 1:0.0056-0.0754.

[0047] Preferably, in step (1), the zinc salt is Zn(CH3COO)2·2H2O.

[0048] Preferably, in step (1), the metal salt is selected from transition metal salts, and more preferably from one or more of copper acetate, iron acetate, cobalt acetate and nickel acetate.

[0049] In some embodiments of the invention, preferably, in step (1), the metal salts are copper acetate, iron acetate, cobalt acetate or nickel acetate.

[0050] In some embodiments of the invention, preferably, in step (1), the mass ratios of Zn(CH3COO)2·2H2O and the metal salt are 1:0.00563, 1:0.0151, 1:0.0133, and 1:0.0664, respectively.

[0051] According to the present invention, in order to accelerate the dissolution of zinc acetate and effectively prevent the solvent from evaporating too quickly, in the preparation method described above, preferably, the dissolution temperature is 80-90°C in step (1).

[0052] In some embodiments of the invention, preferably, the dissolution temperature in step (1) is 80°C.

[0053] Preferably, the alcohol solvent is ethanol.

[0054] According to the present invention, in order to obtain small-sized ZnO quantum dots, preferably, in step (2), the base is KOH; the alcoholic solution of the base is added dropwise, specifically at 2-10 mL / min.

[0055] According to the present invention, in order to ensure sufficient reaction in the preparation method, preferably, in step (2), the mass ratio of Zn(CH3COO)2·2H2O to KOH is 1:0.356-0.374.

[0056] More preferably, in step (2), the mass ratio of Zn(CH3COO)2·2H2O to KOH is 1:0.356.

[0057] Preferably, the reaction in step (2) is carried out in an ice bath.

[0058] According to the present invention, in order to ensure that the metal-doped zinc oxide quantum dot catalyst is completely precipitated in the preparation method, preferably, in step (3), the solvent is n-hexane; the volume ratio of mixed solution II to n-hexane is 1:3-5.

[0059] More preferably, in step (3), the volume ratio of mixed solution II to n-hexane is 1:3.

[0060] According to the present invention, in the preparation method, in step (3), the treatment is centrifugation at 4500-6000 r / min and vacuum drying.

[0061] In some embodiments of the invention, preferably, in step (3), the treatments are: centrifugation at 4500 r / min for 15 min, and vacuum drying at 60°C.

[0062] A third aspect of the present invention provides a metal-doped zinc oxide quantum dot catalyst prepared by the preparation method of the second aspect of the present invention.

[0063] The fourth aspect of the present invention provides an application of the metal-doped zinc oxide quantum dot catalyst of the present invention in the electrochemical reduction reaction of carbon dioxide.

[0064] The fifth aspect of the present invention provides a method for producing syngas from carbon dioxide, wherein the method comprises: performing an electrochemical reduction reaction of carbon dioxide and water in the presence of a metal-doped zinc oxide quantum dot catalyst of the present invention to obtain syngas.

[0065] Under the same reaction conditions, the maximum CO Faraday efficiency obtained by electrocatalyzing CO2 reduction to CO using undoped ZnO quantum dots is 78.4%, and the syngas ratio can be adjusted by controlling the potential (between -0.7 and -1.4 V vs. RHE) between 0.9 and 3.7. When the metal-doped zinc oxide quantum dot catalyst of this invention is applied to the electrochemical reduction of carbon dioxide to generate syngas, the selectivity of the doped ZnO quantum dot catalyst for CO is significantly reduced compared to that of the original ZnO quantum dot catalyst, with the maximum CO Faradaic efficiency decreasing to 68.4% or 64.9%, and the syngas adjustment range narrowing to 0.6-2.2 or 0.8-1.8. However, when Co or Ni is doped with ZnO quantum dots, the selectivity of the doped ZnO quantum dot catalyst for CO is enhanced compared to that of the original ZnO quantum dot catalyst, with the maximum CO Faradaic efficiency increasing to 89.9% or 82.9%, and the syngas adjustment range expanding to 1.3-9 or 1.2-4.8.

[0066] The following examples illustrate the technical solution of the present invention, wherein all raw materials and reagents used are commercially available.

[0067] Zinc acetate dihydrate, purity AR, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0068] Copper acetate, 98.0% purity, purchased from Aladdin Reagent (Shanghai) Co., Ltd.

[0069] Ferric acetate, 98.0% purity, purchased from Aladdin Reagent (Shanghai) Co., Ltd.

[0070] Cobalt acetate, 98.0% purity, purchased from Aladdin Reagent (Shanghai) Co., Ltd.

[0071] Nickel acetate, 98.0% purity, purchased from Aladdin Reagent (Shanghai) Co., Ltd.

[0072] Potassium hydroxide, purity AR, purchased from Sinopharm Chemical Reagent Co., Ltd.

[0073] n-Hexane, 98.0% purity, purchased from Aladdin Reagent (Shanghai) Co., Ltd.

[0074] Comparative Example 1

[0075] Preparation of zinc oxide quantum dots

[0076] (1) Dissolve 5.50g of Zn(CH3COO)2·2H2O in 150mL of anhydrous ethanol solution, and reflux and stir for 2h under 80℃ water bath conditions until the solution is colorless and transparent;

[0077] (2) Place the above solution in an ice bath and add 20 mL of 1.75 mol / L KOH-ethanol solution dropwise, stirring for 8 hours;

[0078] (3) The solution obtained in step (2) was mixed with n-hexane at a volume ratio of 1:3. A large amount of white precipitate appeared. The solution was centrifuged at 4500 r / min for 15 min and dried under vacuum at 60 °C to obtain ZnO quantum dots.

[0079] XRD measurements were performed on ZnO quantum dots. Figure 1 As shown in the XRD pattern, in the crystal structure of ZnO quantum dots, the 2θ value of the diffraction peak of the ZnO(002) plane is 33.20°; and the 2θ value of the diffraction peak of the ZnO(110) plane is 59.33°.

[0080] High-magnification TEM analysis was performed on ZnO quantum dots, and... Figure 2 The TEM image shown indicates that the particle size of the ZnO quantum dots is approximately 5 nm.

[0081] Example 1

[0082] Preparation of copper-doped ZnO quantum dots (Cu-ZnO)

[0083] (1) Dissolve 5.50g of Zn(CH3COO)2·2H2O and 0.031g of copper acetate in 150mL of anhydrous ethanol solution, and reflux and stir for 2h under 80℃ water bath conditions until the solution is colorless and transparent;

[0084] (2) Place the above solution in an ice bath and add 20 mL of 1.75 mol / L KOH-ethanol solution dropwise, stirring for 8 hours;

[0085] (3) The solution obtained in step (2) was mixed with n-hexane at a volume ratio of 1:3. A large amount of white precipitate appeared. The solution was centrifuged at 4500 r / min for 15 min and dried under vacuum at 60 °C to obtain copper-doped ZnO quantum dots.

[0086] XRD measurements were performed on copper-doped ZnO quantum dots. Figure 1 As shown in the XRD pattern, the 2θ value of the diffraction peak of the ZnO(002) plane in the crystal structure of copper-doped ZnO quantum dots is 34.10°; the 2θ value of the diffraction peak of the ZnO(110) plane is 60.09°.

[0087] Copper-doped ZnO quantum dots significantly enhanced the activation of carbon dioxide, achieving high catalytic reductive properties and selectivity. Simultaneously, the proportion of syngas could be controlled over a wide range, which is beneficial for the synthesis of downstream syngas products. TEM analysis showed that the particle size of the copper-doped ZnO quantum dots was approximately 10 nm.

[0088] Example 2

[0089] Preparation of iron-doped zinc oxide quantum dots (Fe-ZnO)

[0090] (1) Dissolve 5.50g of Zn(CH3COO)2·2H2O and 0.083g of ferric acetate in 150mL of anhydrous ethanol solution, and reflux and stir for 2h under 80℃ water bath conditions until the solution is colorless and transparent;

[0091] (2) Place the above solution in an ice bath and add 20 mL of 1.75 mol / L KOH-ethanol solution dropwise, stirring for 8 hours;

[0092] (3) The solution obtained in step (2) was mixed with n-hexane at a volume ratio of 1:3. A large amount of white precipitate appeared. The solution was centrifuged at 4500 r / min for 15 min and dried under vacuum at 60 °C to obtain iron-doped ZnO quantum dots.

[0093] XRD measurements were performed on iron-doped ZnO quantum dots, and the XRD pattern was compared with... Figure 1 Similarly, it can be seen that in the crystal structure of iron-doped ZnO quantum dots, the 2θ value of the diffraction peak of the ZnO(002) plane is 34.93°, and the 2θ value of the diffraction peak of the ZnO(110) plane is 61.13°.

[0094] High-magnification TEM analysis of iron-doped ZnO quantum dots revealed that the particle size of the iron-doped ZnO quantum dots was approximately 10 nm.

[0095] Example 3

[0096] Preparation of cobalt-doped zinc oxide quantum dots (Co-ZnO)

[0097] (1) Dissolve 5.50g of Zn(CH3COO)2·2H2O and 0.073g of cobalt acetate in 150mL of anhydrous ethanol solution, and reflux and stir for 2h under 80℃ water bath conditions until the solution is colorless and transparent;

[0098] (2) Place the above solution in an ice bath and add 20 mL of 1.75 mol / L KOH-ethanol solution dropwise, stirring for 8 hours;

[0099] (3) The solution obtained in step (2) was mixed with n-hexane at a volume ratio of 1:3. A large amount of white precipitate appeared. The solution was centrifuged at 4500 r / min for 15 min and dried under vacuum at 60 °C to obtain cobalt-doped ZnO quantum dots.

[0100] XRD measurements were performed on cobalt-doped ZnO quantum dots, and the XRD pattern was compared with... Figure 1Similarly, it can be seen that in the crystal structure of cobalt-doped ZnO quantum dots, the 2θ value of the diffraction peak of the ZnO(002) plane is 32.66°, and the 2θ value of the diffraction peak of the ZnO(110) plane is 52.59°.

[0101] High-magnification TEM analysis of cobalt-doped ZnO quantum dots revealed that the particle size of the cobalt-doped ZnO quantum dots was approximately 10 nm.

[0102] Example 4

[0103] Preparation of nickel-doped zinc oxide quantum dots (Ni-ZnO)

[0104] (1) Dissolve 5.50g of Zn(CH3COO)2·2H2O and 0.365g of nickel acetate in 150mL of anhydrous ethanol solution, and reflux and stir for 2h under 80℃ water bath conditions until the solution is colorless and transparent;

[0105] (2) Place the above solution in an ice bath and add 20 mL of 1.75 mol / L KOH-ethanol solution dropwise, stirring for 8 hours;

[0106] (3) The solution obtained in step (2) was mixed with n-hexane at a volume ratio of 1:3. A large amount of white precipitate appeared. The solution was centrifuged at 4500 r / min for 15 min and dried under vacuum at 60 °C to obtain nickel-doped ZnO quantum dots.

[0107] XRD measurements were performed on nickel-doped ZnO quantum dots, and the XRD patterns were compared with... Figure 1 Similarly, it can be seen that in the crystal structure of nickel-doped ZnO quantum dots, the 2θ value of the diffraction peak of the ZnO(002) plane is 31.96°, and the 2θ value of the diffraction peak of the ZnO(110) plane is 57.89°.

[0108] High-magnification TEM analysis of nickel-doped ZnO quantum dots revealed that the particle size of the nickel-doped ZnO quantum dots was approximately 10 nm.

[0109] Test Example 1

[0110] The metal-doped zinc oxide quantum dots prepared in Examples 1-4 and the zinc oxide quantum dots prepared in Comparative Example 1 were tested as catalysts to evaluate their catalytic activity, CO selectivity, and the controlled proportion of syngas in the electrochemical reduction reaction of carbon dioxide to generate syngas.

[0111] The test conditions were: the actual reaction area was 2 cm². 2 Electrolysis was performed in a flowing electrolytic cell under constant potential conditions of -0.7 to -1.4V (vs. RHE reversible hydrogen electrode), with a CO2 gas flow rate of 30 sccm and an electrolyte of 0.5 M KHCO3.

[0112] Test results are as follows Figure 3 , 4 Figure 5 shows a comparison of the Faradaic efficiency and syngas ratio of the catalysts before and after doping in the electrochemical reduction of carbon dioxide to produce CO. Undoped zinc oxide quantum dots achieved the highest CO Faradaic efficiency of 78.4% under -0.9 V vs. RHE conditions, and the syngas ratio could be adjusted by controlling the potential (between -0.7 and -1.4 V vs. RHE) between 0.9 and 3.7. The selectivity of Cu-ZnO and Fe-ZnO for CO decreased significantly compared to ZnO. The former achieved a CO Faradaic efficiency of 68.4% under -0.9 V vs. RHE conditions, with the syngas adjustment range narrowing to 0.6–2.2, while the latter achieved a CO Faradaic efficiency of 64.9% under the same conditions, with the syngas adjustment range also narrowing to 0.8–1.8. Co and Ni doped zinc oxide quantum dots enhance the selectivity for CO. Among them, Co-ZnO achieves a CO Faraday efficiency of 89.9% under -0.9V vs. RHE conditions, and the syngas adjustment range is also increased to 1.3-9.

[0113] As can be seen from the above embodiments and test examples, by doping zinc oxide quantum dot catalysts with metal elements, the proportion of syngas can be controlled within a large range, which is beneficial to the synthesis of downstream products of syngas.

[0114] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A metal-doped zinc oxide quantum dot catalyst, characterized in that, Based on the total weight of the metal-doped zinc oxide quantum dot catalyst, the metal-doped zinc oxide quantum dot catalyst contains 95-100 wt% zinc oxide and 1-5 wt% doping metal; and the zinc oxide and doping metal exist in the form of a solid solution. The crystal structure of the metal-doped zinc oxide quantum dot catalyst satisfies the following relationship: 0°<∣A 110 -B 110 |≤1.8°, where A 110 and B 110 The values ​​of 2θ, representing the diffraction peaks of the (110) plane of ZnO, are respectively shown in the XRD spectra of the metal-doped zinc oxide quantum dot catalyst and the XRD spectra of zinc oxide obtained under the same XRD measurement conditions. 0°<∣A 002 -B 002 |≤1.8°, where A 002 and B 002 The values ​​represent the 2θ values ​​of the diffraction peaks on the (002) plane of ZnO, respectively, in the XRD spectra of the metal-doped zinc oxide quantum dot catalyst and the XRD spectra of zinc oxide obtained under the same XRD measurement conditions.

2. The catalyst according to claim 1, wherein, The doped metal is selected from transition metals.

3. The catalyst according to claim 2, wherein, The doped metal is one or more of copper, iron, cobalt, and nickel.

4. The catalyst according to any one of claims 1-3, wherein, The catalyst has an average particle size of 3-15 nm.

5. A method for preparing a metal-doped zinc oxide quantum dot catalyst according to any one of claims 1-4, characterized in that, The method includes: (1) Dissolve the zinc salt and the metal salt in an alcohol solvent to obtain a mixed solution I; (2) The mixed solution I is reacted with an alcoholic solution of alkali to obtain mixed solution II; (3) The mixed solution II is mixed with a solvent and processed to obtain the metal-doped zinc oxide quantum dot catalyst.

6. The preparation method according to claim 5, wherein, In step (1), the mass ratio of zinc salt to metal salt is 1:0.0056-0.0754.

7. The preparation method according to claim 5 or 6, wherein, In step (1), the metal salt is selected from transition metal salts.

8. The preparation method according to claim 7, wherein, In step (1), the metal salt is one or more of copper acetate, iron acetate, cobalt acetate or nickel acetate.

9. The preparation method according to claim 5 or 6, wherein, The zinc salt is Zn(CH3COO)2·2H2O.

10. The preparation method according to claim 5 or 6, wherein, The alcohol solvent is ethanol.

11. The preparation method according to claim 5 or 6, wherein, In step (1), the dissolution temperature is 80-90℃.

12. The preparation method according to claim 5 or 6, wherein, In step (2), the mass ratio of the zinc salt to the alkali is 1:0.356-0.

374.

13. The preparation method according to claim 5 or 6, wherein, During the reaction, the alcoholic solution of the base is added dropwise.

14. The preparation method according to claim 13, wherein, The rate of dropwise addition is 2-10 mL / min.

15. The preparation method according to claim 13, wherein, The alkali is KOH.

16. The preparation method according to claim 5 or 6, wherein, In step (3), the volume ratio of the mixed solution II to the solvent is 1:3-5.

17. The preparation method according to claim 16, wherein, The solvent is n-hexane.

18. The preparation method according to claim 16, wherein, In step (3), the processing procedure includes: centrifuging the product obtained by mixing at a speed of 4500-6000 r / min and then vacuum drying.

19. The application of a metal-doped zinc oxide quantum dot catalyst according to any one of claims 1-4 in the electrochemical reduction reaction of carbon dioxide.

20. A method for producing syngas from carbon dioxide, characterized in that, The method comprises: in the presence of a metal-doped zinc oxide quantum dot catalyst as described in any one of claims 1-4, performing an electrochemical reduction reaction of carbon dioxide and water to obtain syngas.

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