CN118045595A - Reversed phase metal oxide catalyst for preparing methanol by carbon dioxide hydrogenation - Google Patents

Abstract

A reversed phase metal oxide catalyst for preparing methanol by carbon dioxide hydrogenation belongs to the field of carbon neutralization. In one aspect, the application of the reversed-phase metal oxide catalyst in the methanol preparation process by carbon dioxide hydrogenation is provided, the catalyst is filled in a fixed bed reactor, then the mixed gas is introduced with the molar ratio of CO ₂/H₂/N₂ =1/(1.0-5.0)/(0.5-5), the flow rate of the mixed gas is controlled to be 5-100mL/min, the CO ₂ hydrogenation reaction is carried out through the catalyst fixed bed reactor, the reaction temperature is 180-340 ℃, the reaction pressure is 0.1-5MPa, and the conversion rate of CO ₂ and the selectivity of methanol are obtained through gas chromatography detection and calculation of the product. In a second aspect, a method of preparing the catalyst is provided. The catalyst is a novel catalyst for preparing methanol by CO ₂ hydrogenation, and can effectively improve the CO ₂ conversion rate and the selectivity of the methanol.

Description

A reverse metal oxide catalyst for hydrogenation of carbon dioxide to methanol

Technical Field

The invention relates to application of a reverse metal oxide catalyst with zinc oxide loaded on the surface of stable cuprous oxide in a process of producing methanol by hydrogenation of carbon dioxide, and belongs to the field of carbon neutralization.

Background technique

The increase in the _CO2 content in the atmosphere and the development of renewable energy technology have greatly promoted the development of _CO2 capture and utilization research. The liquid product methanol has a high economic value and can be used as a raw material for the preparation of fine chemical products. Methanol is an important basic organic raw material and plays a key role in the manufacture of dimethyl sulfate, dimethyl diformate, pesticides and pharmaceuticals. Methanol is also an important raw material for the production of fine chemical products such as formaldehyde, acetic acid, and methyl formate. Its wide range of uses in chemicals, pharmaceuticals, pesticides, coatings, etc. has greatly promoted the development of methanol production and market demand. Therefore, the catalytic reaction of _CO2 hydrogenation to methanol has attracted much attention.

The catalyst of the present invention is innovative in the catalytic reaction pathway and structure, and has excellent activation and conversion capabilities for _CO2 and _H2 molecules, promotes the generation of methanol products, and reduces the selectivity for byproduct CO. The activity test results of the catalyst applied to _CO2 hydrogenation reaction also show that the catalyst of the present invention has more excellent _CO2 activity and methanol selectivity than ZnO loaded on the surface of metal Cu. It can be seen that the reverse metal oxide catalyst of cuprous oxide loaded zinc oxide prepared by the present invention utilizes the synergistic effect between Cu ⁺ -O-Zn, and effectively improves the adsorption and activation of _H2 and _CO2 . Therefore, it is of great significance to synthesize a Cu-Zn catalyst with high _CO2 conversion rate and high methanol selectivity.

Summary of the invention

The present invention aims at the shortcomings of Cu ⁺ in the reverse metal oxide catalyst for synthesizing stable carbon dioxide hydrogenation to produce methanol, such as thermodynamic instability in a reducing atmosphere or an acidic environment with water, and provides a reverse metal oxide catalyst with zinc oxide loaded on the surface of cuprous oxide. The catalyst is a new catalyst for _CO2 hydrogenation to produce methanol, which can effectively improve the _CO2 conversion rate and the selectivity of methanol.

In the first aspect, the reverse metal oxide catalyst is used in the process of producing methanol by hydrogenating carbon dioxide. The catalyst is filled in a fixed bed reactor, and then a mixed gas with a molar ratio of _CO2 / _H2 / _N2 =1/(1.0-5.0)/(0.5-5) is introduced. The flow rate of the mixed gas is controlled at 5-100mL/min. The _CO2 hydrogenation reaction is carried out in the catalyst fixed bed reactor. The reaction temperature is 180-340°C and the reaction pressure is 0.1-5MPa. The product is detected by gas chromatography and the _CO2 conversion rate and methanol selectivity are obtained by calculation.

In a second aspect, an embodiment of the present invention provides a method for preparing the reverse metal oxide catalyst for hydrogenating carbon dioxide to methanol provided in the embodiment of the first aspect above, the preparation method comprising the following steps:

Step 1: Cu ²⁺ precursor, octadecenoic acid, anhydrous ethanol and water are mixed evenly in a mass ratio of (0.01-5): (0-10): (0-10): (5-20), and stirred at (20-35) ° C for (0.5-6) h.

Step 2: The ^Cu2+ solution, precipitant, reducing agent and water in step 1 are uniformly mixed in a mass ratio of (1-10): (1-20): (1-20): (1-200), stirred for reaction at (50-150)°C for (0.5-20)h, cooled to (20-35)°C, centrifuged and washed with water for multiple times, and then dried in a vacuum drying oven at (50-120)°C for (5-48)h to obtain _Cu2O .

Step 3: The _Cu2O , Zn2 ⁺ precursor and water obtained in step 2 are uniformly mixed in a mass ratio of (1-10): (0.1-2): (1:10), reacted at (25-150)°C for (0.5-20)h, and then dried in a vacuum drying oven at (50-120)°C for (5-48)h, and the dried product is calcined in a _N2 or Ar gas atmosphere at (300-800°C) for 1-10h to obtain ZnO/ _Cu2O .

Optionally, the synthesized cuprous oxide can be tuned to expose a specific crystal face, and the crystals respectively embody rhombic dodecahedron (110), cube (100), octahedron (111), and the size is about 0.5 to 6 μm.

Optionally, the Cu precursor in step 1 includes one of the following compounds:

CuCl ₂ ·2H ₂ O, Cu(CH ₃ COO) ₂ , CuSO ₄ , Cu(NO ₃ ) ₂ ·3H ₂ O

Optionally, the reducing agent in step 1 comprises one of the following compounds:

Glucose, L-ascorbic acid, sodium citrate

Optionally, the precipitant described in step 1 is

NaOH

Optionally, the mass of the Zn metal precursor added in step 2 is 0.01 to 0.2 times the mass of Cu ₂ O.

Compared with the existing technology, the solution provided by the embodiment of the present invention can produce the following beneficial effects:

The cuprous oxide-loaded zinc oxide inverse metal oxide structure provided in the embodiments of the present application has the characteristic of adjustable exposure of a specific single crystal face; the _Cu2O structure that selectively exposes a specific crystal face can maintain the stable presence of Cu ⁺ , provide an effective Cu ⁺ -O-Zn active interface, and promote the adsorption and activation of reactants _CO2 and _H2 at the surface active sites.

In addition, the preparation method provided in this embodiment is simple, the conditions are mild, and it is easy to promote and apply on a large scale. The preparation principle of the cuprous oxide-loaded zinc oxide reverse metal oxide is to first prepare a stable _Cu2O with a certain crystal face exposed by a simple liquid phase reduction method, then impregnate a layer of Zn2 ⁺ precursor on the surface of _Cu2O , and calcine in _N2 or Ar atmosphere to form ZnO/ _Cu2O material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a SEM image of Cu ₂ O prepared in Example 1;

FIG2 is an XRD pattern of Cu ₂ O prepared in Example 1;

FIG3 is an XRD diagram of ZnO loaded on the surface of Cu ₂ O prepared in Example 1;

FIG4 is a graph showing the CO ₂ hydrogenation reaction performance of the Cu ₂ O surface loaded with ZnO prepared in Example 1 and the comparative example metal Cu particle surface loaded with ZnO;

FIG5 is a graph showing the methanol selectivity performance of the ZnO loaded on the surface of Cu ₂ O prepared in Example 1 and the ZnO loaded on the surface of the metal Cu particles of the comparative example.

Detailed ways

Cu-based catalysts are widely used in catalytic processes due to their high _CO2 activation and conversion capabilities. However, research on active species of Cu is still controversial in recent years. During the catalytic reaction, the valence state, morphology, exposed crystal surface, oxygen vacancy concentration and effective active interface of Cu species have a great influence on the activity and selectivity of the product. ZnO, _ZrO2 , _CeO2 , etc. can be used as structure modifiers, hydrogen storage, hydrogen bonding and direct promoters of _CO2 activation. Researchers believe that the excellent _CO2 hydrogenation activity of Cu-based supported metal oxide catalysts may be due to the close synergistic effect between Cu and metal oxides at the interface. This interface can produce a large number of Cu ⁺ -OM active sites, which can simultaneously adsorb and activate _H2 and _CO2 , promote the formation of methanol, and thus improve the selectivity of methanol and the conversion rate of _CO2 .

Usually cuprous oxide can stably exist in dry air and is almost unaffected by temperature. However, cuprous ions are easily reduced to metallic copper in a reducing atmosphere with _H2 or an acidic environment with _CO2 and water. Therefore, the present invention directly synthesizes relatively stable cuprous oxide by a simple liquid phase reduction method, then impregnates a precursor of a zinc species, and roasts in an _N2 or Ar atmosphere to obtain a stable zinc oxide-supported cuprous oxide catalyst. The catalyst of the present invention has a large number of Zn-O-Cu ⁺ active sites. Moreover, a byproduct CO is easily generated during the _CO2 hydrogenation reaction, and Cu ⁺ has a strong adsorption capacity for CO, which can promote the path of CO hydrogenation to methanol, thereby improving the selectivity of methanol.

The catalyst provided in the examples of the present application is specifically a reverse metal oxide catalyst in which zinc oxide is loaded on the surface of a cuprous oxide carrier.

The addition of octadecenoic acid and octadecenoic acid as a surfactant in the catalyst provided in the examples of the present application has an indispensable influence on the formation of the (110) crystal face, and anhydrous ethanol is used as a solvent for octadecenoic acid. No addition is required during the synthesis of the (100) and (111) crystal faces of Cu ₂ O.

The catalyst provided in the embodiments of the present application has the characteristic of adjustable exposure of a specific single crystal face. The _Cu2O structure that selectively exposes a specific crystal face can maintain the stable existence of Cu ⁺ , provide an effective Zn-O-Cu ⁺ active interface, and promote the adsorption and activation of reactants _CO2 and _H2 at the surface active sites.

In addition, the preparation method provided in this embodiment is simple, the conditions are mild, and it is easy to promote and apply on a large scale. The preparation principle of the cuprous oxide surface-loaded zinc oxide reverse metal oxide is to first prepare a stable _Cu2O with a certain crystal face exposed by a simple liquid phase reduction method, then impregnate a layer of Zn2 ⁺ precursor on the surface of _Cu2O , and calcine in _N2 or Ar atmosphere to form ZnO/ _Cu2O material.

The invention discloses an application of a zinc oxide reverse metal oxide catalyst supported on the surface of cuprous oxide in a process of preparing methanol by hydrogenation of carbon dioxide. The catalyst is filled in a fixed bed reactor, and then a mixture of _CO2 / _H2 / _N2 having a molar ratio of 1/(1.0-5.0)/(0.5-5) is introduced, and the flow rate of the mixed gas is controlled at 5-100 mL/min. The _CO2 hydrogenation reaction is carried out in the catalyst fixed bed reactor, the reaction temperature is 180-340°C, the reaction pressure is 0.1-5 MPa, the product is detected by gas chromatography, and the _CO2 conversion rate and methanol selectivity are obtained by calculation.

The preparation method of the cuprous oxide surface-supported zinc oxide reverse metal oxide catalyst provided in an embodiment of the present invention comprises the following steps:

Step 1: Cu ²⁺ precursor, octadecenoic acid, anhydrous ethanol and water are mixed evenly in a mass ratio of (0.01-5): (0-10): (0-10): (5-20), and stirred at (20-35) ° C for (0.5-6) h.

Step 2: The ^Cu2+ solution, precipitant, reducing agent and water in step 1 are uniformly mixed in a mass ratio of (1-10): (1-20): (1-20): (1-200), stirred for reaction at (50-150)°C for (0.5-20)h, cooled to (20-35)°C, centrifuged and washed with water for multiple times, and then dried in a vacuum drying oven at (50-120)°C for (5-48)h to obtain _Cu2O .

Step 3: The _Cu2O , Zn2 ⁺ precursor and water obtained in step 2 are uniformly mixed in a mass ratio of (1-10): (0.1-2): (1:10), reacted at (25-150)°C for (0.5-20)h, and then dried in a vacuum drying oven at (50-120)°C for (5-48)h, and the dried product is calcined in a _N2 or Ar gas atmosphere at (300-800°C) for 1-10h to obtain ZnO/ _Cu2O .

Optionally, the synthesized cuprous oxide can be tuned to expose a specific crystal face, and the crystals respectively embody rhombic dodecahedron (110), cube (100), octahedron (111), and the size is about 0.5 to 6 μm.

Optionally, the Cu precursor in step 1 includes one of the following compounds:

CuCl ₂ ·2H ₂ O, Cu(CH ₃ COO) ₂ , CuSO ₄ , Cu(NO ₃ ) ₂ ·3H ₂ O

Optionally, the reducing agent in step 1 comprises one of the following compounds:

Glucose, L-ascorbic acid, sodium citrate

Optionally, the precipitant described in step 1 is

NaOH

Optionally, the mass of the Zn metal precursor added in step 2 is 0.01 to 0.2 times the mass of Cu ₂ O.

The preparation process of the cuprous oxide-loaded zinc oxide reverse metal oxide structure is described in detail below with reference to several specific examples.

Example 1: Preparation of a reverse metal oxide structure with zinc oxide loaded on the surface of cuprous oxide

0.36g of anhydrous CuSO ₄ , 12mL of octadecenoic acid, 60mL of anhydrous ethanol and 120mL of water were added to the reactor and mixed evenly at 90°C. Then, the mixed solution, 0.32g of NaOH, 3.4g of glucose and 120mL of water were mixed evenly, reacted at 90°C for 1h, cooled to 25°C, centrifuged, washed with water and anhydrous ethanol, and vacuum dried at 60°C for 10h to obtain Cu ₂ O with an exposed (110) crystal face of about 1.2μm. The morphology of Cu ₂ O is shown in Figure 1. Cu ₂ O exhibits a perfect rhombic dodecahedron morphology and a smooth surface. The size is 1.2μm _{. The structure of Cu 2 O} is shown in Figure 2. The diffraction peak of Cu ₂ O can be observed. Figures 1 and 2 prove that Cu ₂ O was successfully synthesized.

1 g of the Cu ₂ O obtained above was weighed and mixed with 1 mL of water by ultrasonic, added to a container and stirred at 25°C for 6 h, then 0.0916 g of Zn(NO ₃ ) ₂ ·6H ₂ O was added and impregnated for 12 h, then stirred at 35°C for 10 h, and vacuum dried at 60°C for 6 h. Then, it was calcined at 350°C for 3 h under Ar atmosphere to obtain a ZnO/Cu ₂ O-(110) structure. The ZnO/Cu ₂ O rhombic dodecahedron structure is shown in Figure 3. After loading ZnO, we did not find the diffraction peak of Zn, indicating that the ZnO nanoclusters are small in size and uniformly dispersed.

Comparative Example 1: Preparation of ZnO structure loaded on metal Cu surface

2 g of Cu ₂ O synthesized in the example was weighed directly and placed in a magnetic boat, then calcined in a tube furnace at 400° C. for 4 h in a 10% H ₂ /Ar mixed gas atmosphere (flow rate of 30 mL/min) with a heating rate of 5° C./min. Cooled to 25° C. to obtain a metal Cu catalyst carrier.

1 g of the obtained metal Cu carrier was weighed and ultrasonically dispersed in 1 mL of water, and 0.1 g of Zn(NO ₃ ) ₂ ·6H ₂ O was added and impregnated and stirred at 25°C for 10 h, and then placed in an oven to dry for 6 h. Finally, the sample was calcined at 400°C in a N ₂ or Ar atmosphere for 4 h, with the heating rate controlled at 5°C/min to obtain a metal Cu surface-loaded ZnO structure (ZnO/Cu).

The Cu ₂ O-(110) surface-supported ZnO and metal Cu surface-supported ZnO samples obtained in Example 1 were subjected to CO ₂ hydrogenation catalytic reaction. 0.2 g of the Cu ₂ O surface-supported ZnO sample was placed in a fixed bed reactor. Methanol was produced under the conditions of CO ₂ /H ₂ /N ₂ (V _CO2 :V _H2 :V _N2 =22%:66%:12%) mixed gas, 3 MPa pressure, 180-300°C reaction temperature, and 15000 mL g _cat ^-1 h ^-1 space velocity. The product was detected by gas chromatography to obtain CO ₂ conversion rate and methanol selectivity, and the catalytic performance diagram of Example 1 and the comparative example as shown in FIG4 was obtained. The prepared Cu ₂ O surface-supported ZnO sample had significantly improved CO ₂ hydrogenation catalytic performance than the metal Cu surface-supported ZnO sample. At 300°C, the CO ₂ conversion rate was as high as 21.15%, which was higher than that of the metal Cu surface-supported ZnO (17.35%). Figure 5 shows the change of methanol selectivity with temperature. The prepared Cu ₂ O surface-supported ZnO sample has a methanol selectivity 10% higher than that of the metal Cu particle surface-supported ZnO sample. Figures 4 and 5 show that the Cu ₂ O surface-supported ZnO sample has good CO ₂ conversion rate and methanol selectivity.

Example 2

The preparation method of a cuprous oxide surface-loaded zinc oxide reverse metal oxide structure comprises the following steps:

0.171 g of anhydrous CuCl ₂ ·2H ₂ O and 100 mL of water were added to the reactor and mixed evenly in an oil bath at 90°C. Then, the above solution, 1 g of NaOH, 1.06 g of ascorbic acid and 22 mL of water were mixed evenly, reacted for 3 h, cooled to 25°C, centrifuged with water and anhydrous ethanol, washed, and dried in a vacuum at 60°C for 12 h to obtain Cu ₂ O cubes with an exposed (100) crystal face of about 0.8 μm.

1 g of the Cu ₂ O obtained above was weighed and mixed with 1 mL of water by ultrasonic, added to a container and stirred at 35°C, then 0.1 g of Zn(NO ₃ ) ₂ ·6H ₂ O was added and stirred and impregnated at 35°C for 12 h, and vacuum dried at 60°C for 12 h. Then, it was calcined at 350°C for 3 h in an Ar atmosphere to obtain a ZnO/Cu ₂ O-(100) structure.

By carrying out _CO2 hydrogenation catalytic reaction on the _Cu2O- (100) surface-loaded ZnO sample obtained in Example 2, 0.2 g of the _Cu2O- (100) surface-loaded ZnO sample was placed in a fixed bed reactor, and methanol was produced under the conditions of _CO2 / _H2 / _N2 ( _VCO2 : _VH2 : _VN2 =22%:66%:12%) mixed gas, 3 MPa pressure, 180-300°C reaction temperature, and 15000 mL _gcat ^-1 h ^-1 space velocity. The _CO2 conversion rate and methanol selectivity of the product were obtained by gas chromatography. At 300°C, the _CO2 conversion rate of the _Cu2O surface-loaded ZnO structure was increased by 5% compared with the _CO2 conversion rate of the metal Cu particle surface-loaded ZnO structure, and the methanol selectivity was increased by 10%.

Example 3

The preparation method of a cuprous oxide surface-loaded zinc oxide reverse metal oxide structure comprises the following steps:

0.24 g of anhydrous CuSO ₄ , 16 mL of octadecenoic acid, 60 mL of anhydrous ethanol and 120 mL of water were added to a three-flask and mixed evenly, and then mixed evenly in a 90°C oil bath. Then, the above solution, 0.32 g of NaOH, 3.2 g of glucose and 120 mL of water were mixed evenly, reacted for 5 h, cooled to 25°C, and the water and anhydrous ethanol were centrifuged, washed, and vacuum dried at 60°C overnight to obtain Cu ₂ O rhombic dodecahedrons with an exposed (110) crystal face of about 1.0 μm.

1 g of the Cu ₂ O obtained above was weighed and mixed with 1 mL of water by ultrasonication, added into a container and stirred at 25°C for 6 h, then 0.2 g of Zn(NO ₃ ) ₂ ·6H ₂ O was added and impregnated for 12 h, then stirred at 35°C for 10 h, and vacuum dried at 60°C for 6 h. Then, it was calcined at 350°C for 3 h in an Ar atmosphere to obtain a ZnO/Cu ₂ O-(110) structure.

By carrying out _CO2 hydrogenation catalytic reaction on the _Cu2O- (100) surface-loaded ZnO sample obtained in Example 3, 0.2 g of the _Cu2O- (110) surface-loaded ZnO sample was placed in a fixed bed reactor, and methanol was produced under the conditions of _CO2 / _H2 / _N2 ( _VCO2 : _VH2 : _VN2 =22%:66%:12%) mixed gas, 3 MPa pressure, 180-300°C reaction temperature, and 15000 mL _gcat ^-1 h ^-1 space velocity. The _CO2 conversion rate and methanol selectivity of the product were obtained by gas chromatography. At 300°C, the _CO2 conversion rate of the _Cu2O surface-loaded ZnO structure was increased by 6% compared with the _CO2 conversion rate of the metal Cu particle surface-loaded ZnO structure, and the methanol selectivity was increased by 12%.

Example 4

The preparation method of a cuprous oxide surface-loaded zinc oxide reverse metal oxide structure comprises the following steps:

3 g of anhydrous Cu(CH ₃ COO) ₂ and 20 mL of water were added to the reactor and mixed and stirred for 1 h. Then the above solution, 5 g of NaOH, 0.58 g of glucose and 30 mL of water were mixed and stirred in a 70°C oil bath for 3 h, cooled to 35°C, centrifuged with water and anhydrous ethanol, washed, and vacuum dried at 60°C for 10 h to obtain Cu ₂ O octahedra with exposed (111) crystal faces of about 1.5 μm.

1g of Cu ₂ O-(111) obtained above and 1mL of water were ultrasonically mixed and added to a container and stirred at 35°C, and then 0.1g of Zn(NO ₃ ) ₂ ·6H ₂ O was added and stirred and impregnated at 35°C for 12h, and vacuum dried at 60°C for 6h. Then, it was calcined at 350°C for 3h in an Ar atmosphere to obtain a ZnO/Cu ₂ O-(111) structure.

The Cu ₂ O-(111) surface-loaded ZnO sample obtained in Example 4 was subjected to a CO ₂ hydrogenation catalytic reaction, and 0.2 g of the Cu ₂ O-(111) surface-loaded ZnO sample was placed in a fixed bed reactor. Methanol was produced under the conditions of a CO ₂ /H ₂ /N ₂ (V _CO2 :V _H2 :V _N2 =22%:66%:12%) mixed gas, 3 MPa pressure, 180-300°C reaction temperature, and 15000 mL g _cat ^-1 h ^-1 space velocity. The CO ₂ conversion rate and methanol selectivity of the product were obtained by gas chromatography. At 300°C, the CO ₂ conversion rate of the Cu ₂ O surface-loaded ZnO structure was increased by 4% compared with the CO ₂ conversion rate of the metal Cu particle surface-loaded ZnO structure, and the methanol selectivity was increased by 8%.

Claims (7)

1. The preparation method of the reversed-phase metal oxide catalyst for preparing methanol by hydrogenating carbon dioxide is characterized by comprising the following steps of:

step 1: cu ²⁺ precursor, octadecenoic acid, absolute ethyl alcohol and water according to mass ratio (0.01-5): (0-10): (0-10): uniformly mixing (5-20) to obtain a Cu ²⁺ -containing solution, and stirring (0.5-6) for h at the temperature of (20-35);

Step 2: step 1 comprises Cu ²⁺ solution, precipitant, reducing agent and water according to the mass ratio (1-10): (1-20): (1-20): uniformly mixing (1-200), stirring and reacting (0.5-20) for h at the temperature of (50-150), cooling to (20-35), centrifuging and washing for multiple times by adopting water, and drying (5-48) for h in a vacuum drying oven at the temperature of (50-120) to obtain Cu ₂ O;

Step 3: and (2) mixing the Cu ₂O、Zn²⁺ precursor obtained in the step (2) with water according to the mass ratio of (1-10): (0.1-2): (1:10) uniformly mixing, reacting for (0.5-20) h at the temperature of (25-150), then drying for (5-48) h in a vacuum drying oven at the temperature of (50-120), and roasting the dried product for 1-10 h at the temperature of 300-800 ℃ under the atmosphere of N ₂ or Ar gas to obtain ZnO/Cu ₂ O.

2. The method according to claim 1, wherein the Cu precursor is one of the following compounds ：CuCl₂·2H₂O、Cu(CH₃COO)₂、CuSO₄、Cu(NO₃)₂·3H₂O.

3. The method of claim 1, wherein the reducing agent of step 1 comprises one of the following compounds: glucose, L-ascorbic acid, sodium citrate.

4. The method of claim 1, wherein the precipitant is NaOH.

5. The method according to claim 1, wherein the mass of the Zn ²⁺ precursor in step 2 is 0.01 to 0.2 times the mass of Cu ₂ O.

6. The method of claim 1, wherein a particular crystal plane is adjustably exposed, the crystals each exhibiting a rhombohedral dodecahedron (110), a cube (100), an octahedral (111) and a size of about 0.5 μm to about 6 μm.

7. The catalyst prepared by the method according to claim 1-6, wherein the molar ratio of CO ₂/H₂/N₂ =1/(1.0-5.0)/(0.5-5) is introduced in the CO ₂ hydrogenation catalytic reaction, the flow rate of the mixed gas is controlled to be 5-100mL/min, the CO ₂ hydrogenation reaction is carried out by a catalyst fixed bed reactor, the reaction temperature is 180-340 ℃, the reaction pressure is 0.1-5MPa, and the conversion rate of CO ₂ and the selectivity of methanol are obtained by detecting and calculating the product by gas chromatography.