Heterogeneous nanocatalysts for CO2 catalytic hydrogenation to methanol and their preparation methods

Abstract

This invention discloses a heterogeneous nanocatalyst for the catalytic hydrogenation of CO2 to methanol and its preparation method. The catalyst precursor comprises a CuO-ZnO composite oxide and highly dispersed Ga, which, after reduction activation, forms a heterogeneous interface structure composed of metallic Cu, ZnO, and Ga. The preparation includes: preparing the CuO-ZnO composite oxide using a co-precipitation method, then ball-milling and mixing it with solid metallic Ga to obtain the precursor, and finally activating it through in-situ photoreduction. This catalyst, when used in the CO2 hydrogenation reaction under photothermal synergistic conditions, significantly improves catalytic activity and methanol selectivity through multi-component interfacial synergy and photothermal effects.

Description

Technical Field

[0001] This invention relates to the field of catalysts, and more specifically to heterogeneous nanocatalysts for the catalytic hydrogenation of CO2 to methanol and their preparation methods. Background Technology

[0002] Methanol is an important basic chemical raw material, widely used in the production of formaldehyde, dimethyl ether, and other products. It also serves as a clean fuel and hydrogen carrier, playing an irreplaceable role in the chemical and energy sectors. Currently, methanol is mainly produced from fossil fuels (coal and natural gas), which not only consumes non-renewable resources but also emits large amounts of CO2. However, using CO2 and H2 to produce methanol can recycle industrial CO2 emissions. Furthermore, if H2 is generated through water electrolysis, a zero-carbon cycle of "green hydrogen-green methanol" can be achieved, alleviating the energy crisis and contributing to the "dual carbon" goals. This has significant strategic importance for promoting energy structure transformation and ecological environmental protection.

[0003] The catalyst is one of the key factors in the process of producing methanol from CO2 and H2. Traditional ternary composite catalysts (such as Cu / ZnO / Al2O3) are the mainstream choice for the hydrogenation of CO2 to methanol, but they have obvious limitations: Cu active particles are prone to sintering and carbon deposition on the surface during the reaction, leading to rapid activity decay; and they have weak ability to inhibit reverse water-gas shift and methanation side reactions, resulting in low methanol selectivity. Therefore, their efficiency and stability in methanol production need to be improved.

[0004] CN120381852B discloses a CuZn-based composite catalyst for the production of lower alcohols from syngas and its preparation method. The oxygen vacancy-modified solvent, by introducing Ga, can effectively control the oxygen vacancy content in the CuZn catalyst. However, the preparation method is complex, and the catalyst performance is relatively low. CN119368190A discloses a method for preparing a CuZnAlGa-based hydrotalcite-derived catalyst for the production of methanol from carbon dioxide-rich syngas. The hydrotalcite-like structure acts as a lattice confinement mechanism to prevent Cu particle aggregation, and the interaction between Cu and oxides improves the adsorption capacity of CO and CO2 on the catalyst surface, enhancing the activity and stability of the production of methanol from CO2-rich syngas. However, due to limitations in the characteristics of the hydrotalcite-like precursor, the inherent properties of the elements, and the adaptability to reaction conditions, it still suffers from insufficient activity and stability, decreased high-temperature selectivity, and high preparation costs.

[0005] In view of this, there is an urgent need for novel methanol synthesis catalysts that can overcome the above-mentioned defects. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a heterogeneous nanocatalyst for the catalytic hydrogenation of CO2 to methanol. This catalyst utilizes the combined effects of multi-component interfacial synergy and photothermal effects to improve catalytic efficiency and methanol selectivity from both energy supply and reaction pathway regulation perspectives. The preparation method of this invention involves introducing solid Ga through ball milling and combining it with in-situ photoreduction to construct a Cu / ZnO / Ga heterogeneous interface, achieving highly efficient and selective hydrogenation of CO2 to methanol under photothermal synergy.

[0007] This invention provides a heterogeneous nanocatalyst for the catalytic hydrogenation of CO2 to methanol, wherein the precursor comprises a CuO-ZnO composite oxide and Ga, and Ga is distributed therein in a highly dispersed state; after reduction and activation, the precursor forms a heterogeneous interface structure comprising metals Cu, ZnO and Ga; wherein the molar ratio of Cu to Zn is 3:(0.5~2), and the mass ratio of the CuO-ZnO composite oxide to Ga is 20:(1~5).

[0008] As an example, the molar ratio of Cu to Zn is 6:1, 5:2, or 3:2.

[0009] As an example, the mass ratio of the CuO-ZnO composite oxide to Ga is 20:1, 20:3, or 20:5.

[0010] The present invention also provides a method for preparing heterogeneous nanocatalysts according to any one of the foregoing descriptions, comprising: CuO-ZnO composite oxides were prepared by co-precipitation method; The obtained CuO-ZnO composite oxide was physically ball-milled with metallic Ga to obtain the precursor of the heterogeneous nanocatalyst; wherein the metallic Ga was solidified before ball milling and remained solid during ball milling.

[0011] As an example, Cu-containing 2+ and Zn 2+ A mixed salt solution and a precipitant were added dropwise to a reaction vessel in parallel flow. The precipitation temperature was controlled at 60-80 °C, and the final pH of the precipitation was 6.5-8.5, resulting in a precipitated slurry. The precipitated slurry was aged at 70-90 °C for 1-3 hours, and after solid-liquid separation, washing, and drying, it was calcined at 300-400 °C for 2-4 hours to obtain the CuO-ZnO composite oxide.

[0012] Optionally, the physical ball milling is carried out under an inert atmosphere, with a ball-to-material ratio of (10~20):1, a ball milling speed of 300-500 rpm, a ball milling time of 5~10 hours, and a ball milling process temperature controlled below 25 ℃.

[0013] Optionally, the ball-to-material ratio is 10:1, 15:1, or 20:1.

[0014] As an example, the preparation method of the heterogeneous nanocatalyst further includes in-situ photoreduction treatment of the precursor of the heterogeneous nanocatalyst; the in-situ photoreduction treatment method is as follows: in a reducing atmosphere containing H2, under a light intensity of 1~3.0 W·cm -2 Under these conditions, the temperature is raised to 200~250 ℃ and maintained for 1~4 hours.

[0015] Preferably, the light intensity is 1.0 W·cm. -2 The reduction temperature was 230 ℃ and the reduction time was 2 hours.

[0016] The present invention further provides a method for producing methanol by catalytic hydrogenation of CO2 using any of the heterogeneous nanocatalysts described above. Under the action of light irradiation, heating and the catalyst that has undergone in-situ photoreduction treatment, a mixed reaction gas of H2 and CO2 is introduced to carry out a photothermal synergistic catalytic hydrogenation reaction to produce methanol.

[0017] As an example, the conditions for the hydrogenation reaction are: reaction temperature 220~260 ℃, reaction pressure 2~5 MPa, volume ratio of H2 to CO2 of the reaction gas (2~4):1, and space velocity 3600~5000 h⁻¹. -1 Preferably, the reaction temperature is 240 °C, the reaction pressure is 3 MPa, the volume ratio of H2 to CO2 in the reaction gases is 3:1, and the space velocity is 3600 h⁻¹. -1 .

[0018] As an example, the light source is a full-spectrum LED light source with an illuminance of 0.5~3.0 W·cm. -2 Preferably, the light intensity is 1.0 W·cm. -2 .

[0019] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a co-precipitation combined with ball milling process. First, CuO-ZnO composite oxide is synthesized via co-precipitation, and then Ga component is introduced through physical ball milling. This method is simple, uses readily available raw materials, and achieves high dispersion of Ga, laying the structural foundation for constructing multi-component heterogeneous interfaces.

[0020] 2. Before use, the catalyst of this invention requires in-situ photoreduction treatment. Metallic Cu nanoparticles are dispersed on a ZnO matrix and form an interface with Ga, constituting a "Cu / ZnO / Ga" heterogeneous structure. This process simultaneously achieves active phase generation, efficient interface construction, and photothermal system adaptation. During the reaction, the system utilizes the photothermal effect to achieve precise energy supply and electronic state control: leveraging the plasma effect of Cu and the photoresponse characteristics of Ga, light energy is converted into localized heat energy, forming a temperature gradient of "locally high temperature at active sites - overall low temperature of the system." This reduces the activation energy of the reaction, saves energy consumption, and avoids side reactions such as reverse water-gas shift (RWGS) and methanation caused by high temperatures. Photoinduced electron transfer can precisely control the electronic state of the catalytic interface, enhancing the dissociation ability of Cu sites for H2 on the one hand, and reducing the adsorption energy of the Ga-modified ZnO surface for the key intermediate HCOO* on the other hand, while simultaneously weakening the adsorption strength of the CH3* intermediate. This multi-effect synergistic mechanism effectively suppresses competing side reactions such as reverse water-gas shift (generating CO) and methanation (generating CH4) along the reaction kinetic pathway, thereby significantly promoting the highly selective directional synthesis of methanol.

[0021] 3. To address the insufficient CO2 activation capacity of traditional single-active-site catalysts, this catalyst achieves functional division and synergy by constructing a Cu / ZnO / Ga heterogeneous interface: Cu, as the main active component, is responsible for adsorbing and dissociating H2 to generate highly active H* species, which then migrate to the ZnO surface via the interface; ZnO adsorbs and activates CO2 through its surface basic sites, weakening the C=O bond; Ga, in a highly dispersed state, regulates the number and intensity of basic sites on the ZnO surface, promoting the reaction of active H* species with CO2 to generate HCOO* intermediates, while simultaneously enhancing the interfacial interaction between ZnO and Cu, and improving catalyst stability through its fluidity and dispersibility. This synergistic pathway of "Cu hydrogen donation → ZnO (Ga regulation) carbon fixation → interfacial hydrogenation" achieves the directional transformation of intermediates, avoiding the retention of active species on the surface of a single component and preventing side reactions.

[0022] 4. The catalyst of the present invention achieves spatial division of active sites through heterogeneous structure, completes the directional transfer and transformation of intermediates through interfacial synergy, and combines photothermal effect to dual regulation of energy and electronic state, thereby reducing the activation energy and overall energy consumption of the reaction from the energy level, suppressing side reactions and promoting the selective generation of methanol from the reaction pathway level, thus breaking through the bottleneck of low activity and many side reactions of traditional catalysts, and realizing the efficient hydrogenation of CO2 to methanol.

[0023] 5. The catalyst described in this invention has photoresponsive characteristics and is suitable for photothermal synergistic catalytic CO2 hydrogenation reaction. Attached Figure Description

[0024] Figure 1This is an EDS mapping image of the catalyst sample prepared in Example 1 of this invention.

[0025] Elemental distribution analysis results of catalyst samples in other embodiments and Figure 1 resemblance. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] The formation mechanism of the active phase of the catalyst in this invention is as follows: The catalyst precursor of this invention is a CuO-ZnO composite oxide obtained through co-precipitation and calcination. In the subsequent in-situ photoreduction activation process, under H2 atmosphere and light irradiation, the CuO component is selectively reduced to metallic Cu nanoparticles, while the ZnO component, due to its higher thermodynamic stability, retains its oxide state under these conditions. Metallic Ga remains in a highly dispersed metallic state throughout the process.

[0028] Therefore, the final active catalyst is a heterogeneous nanocomposite system with rich interfaces, composed of Cu nanoparticles, ZnO oxide, and Ga. Oxygen, primarily present in the ZnO lattice, plays a crucial role in the adsorption and activation of CO2.

[0029] In this invention, the core role of the photothermal effect is not merely to provide heat to the reaction system, but more importantly, to precisely control the electronic structure and energy state of the Cu / ZnO / Ga interface at the nanoscale by exciting the active sites on the catalyst surface with photons. This leads to a dual effect distinct from traditional thermocatalysis: chemically, it promotes the adsorption and activation of CO2, lowers the formation energy barrier of key intermediates (such as HCOO*), and simultaneously suppresses side reactions such as reverse water-gas shift reaction along the reaction pathway; in terms of energy form, it efficiently converts light energy into localized heat confined around the active sites through the plasma effect of Cu and the photoresponse characteristics of Ga, achieving a unique state of microscopic high heat at the active sites and macroscopic low temperature in the reaction system. The latter significantly reduces the overall energy consumption of the reaction, while the former, namely the electronic state modulation of the intrinsic catalytic performance by light, is the fundamental reason for achieving high efficiency and high selectivity, and is also the core advantage of photothermal catalysis over traditional thermocatalysis.

[0030] Example 1 (1) The molar ratio of copper and zinc components is 6:1, and the mass ratio of CuO-ZnO composite oxide to Ga is 20:1.

[0031] Prepare 0.125 mol·L⁻¹ solutions respectively. -1 A mixed salt solution was prepared by mixing 100 mL of Cu(NO3)2·6H2O solution, 16.67 mL of Zn(NO3)2·6H2O solution, and 16.67 mL of Na2CO3 solution. The copper-zinc salt solution and Na2CO3 solution were then simultaneously added dropwise to a three-necked flask using a peristaltic pump. The precipitation temperature was controlled at 70 °C, and the pH of the precipitation was 7.0, resulting in mixed slurry A. After the addition was complete, the mixture was aged at 80 °C for 2 h to obtain a blue-green suspension.

[0032] (2) The suspension was vacuum filtered, and the filter cake was washed four times with deionized water. The filter cake was then transferred to a vacuum drying oven and dried at 100 °C for 10 h to obtain the catalyst precursor. The dried precursor was placed in a muffle furnace and calcined at 350 °C for 3 h in air atmosphere at a heating rate of 5 °C·min. -1 After natural cooling, it is ground into fine powder to obtain CuO-ZnO composite oxide (denoted as CZ).

[0033] (3) With a ball-to-powder ratio of 10:1, place 2 g of CZ powder, 0.1 g of Ga, and 21 g of grinding balls into a ball mill jar. Vacuum the ball mill jar through a valve, and then fill it with inert argon gas. Securely install the ball mill jar onto a planetary ball mill. Start the cooling system to ensure that the jar temperature is maintained below 25 °C (e.g., 25 °C) during the ball milling process to keep gallium in a solid state and ensure effective ball milling dispersion. Set the ball mill speed to 300 rpm and the ball milling time to 7 h.

[0034] (4) After the ball milling process is completed, wait for the ball mill jar to cool completely to room temperature before opening it. Pour the powder and grinding balls in the jar into a sieve to separate the powder product and obtain the CuO-ZnO-Ga composite precursor.

[0035] (5) Transfer 0.2 g of CuO-ZnO-Ga composite precursor to a quartz reaction tube, compact it, and place it in the photothermal reaction system to complete the loading. Close all valves of the reaction system, use a vacuum pump to evacuate the vacuum in the reaction tube to ≤1 Pa, and then introduce Ar (flow rate 50 mL·min). -1 Purge for 30 minutes to remove air and moisture from the system.

[0036] (6) The gas was switched to a 10% H2 / Ar mixture at a flow rate of 45 mL·min. -1Turn on the full-spectrum LED light source and adjust the light intensity to 1.0 W·cm. -2 At the same time, at 2 ℃·min -1 The temperature was raised to 230 °C and maintained for 2 h to complete the in-situ photoreduction (during this process, CuO in the precursor was reduced to metallic Cu nanoparticles, which together with unreduced ZnO and highly dispersed Ga formed a Cu / ZnO / Ga heterogeneous interface active structure).

[0037] Elemental distribution analysis of the prepared catalyst samples was performed using energy dispersive spectroscopy (EDS), and the results are as follows: Figure 1 As shown, the mapping images of Cu (blue), Zn (purple), and Ga (red) show that the three elements are highly dispersed, with no obvious local enrichment or element segregation observed, indicating that the element distribution is relatively uniform.

[0038] (7) After the reduction is complete, maintain a light intensity of 1.0 W·cm. -2 The temperature was raised to 240 °C, the 10% H2 / Ar flow was turned off, and the reaction gases were switched to CO2 and H2, with an H2:CO2 ratio of 3:1 and a reaction space velocity of 3600 h⁻¹. -1 Simultaneously, the system pressure is slowly increased to 3 MPa to start the reaction.

[0039] Example 2 (1) The molar ratio of copper and zinc components is 5:2, and the mass ratio of CuO-ZnO composite oxide to Ga is 20:1.

[0040] Prepare 0.125 mol·L⁻¹ solutions respectively. -1 A mixed salt solution was prepared by mixing 100 mL of Cu(NO3)2·6H2O solution with 40 mL of Zn(NO3)2·6H2O solution to form a mixed salt solution. The copper-zinc salt solution and the Na2CO3 solution were simultaneously added dropwise to a three-necked flask using a peristaltic pump, controlling the precipitation temperature at 70 °C and the precipitation pH at 7.0, resulting in mixed slurry A. After the addition was complete, the mixture was aged at 80 °C for 2 h to obtain a blue-green suspension.

[0041] (2) The suspension was vacuum filtered, and the filter cake was washed four times with deionized water. The filter cake was then transferred to a vacuum drying oven and dried at 100 °C for 10 h to obtain the catalyst precursor. The dried precursor was placed in a muffle furnace and calcined at 350 °C for 3 h in air atmosphere at a heating rate of 5 °C·min. -1 After natural cooling, it is ground into fine powder to obtain CuO-ZnO composite oxide (denoted as CZ).

[0042] (3) With a ball-to-powder ratio of 10:1, place 2 g of CZ powder, 0.1 g of Ga, and 21 g of grinding balls into a ball mill jar. Vacuum the ball mill jar through a valve, and then fill it with inert argon gas. Securely install the ball mill jar onto a planetary ball mill. Start the cooling system to ensure that the jar temperature is maintained below 25 °C (e.g., 25 °C) during the ball milling process to keep gallium in a solid state and ensure effective ball milling dispersion. Set the ball mill speed to 300 rpm and the ball milling time to 7 h.

[0043] (4) After the ball milling process is completed, wait for the ball mill jar to cool completely to room temperature before opening it. Pour the powder and grinding balls in the jar into a sieve to separate the powder product and obtain the CuO-ZnO-Ga composite precursor.

[0044] (5) Transfer 0.2 g of CuO-ZnO-Ga composite precursor to a quartz reaction tube, compact it, and place it in the photothermal reaction system to complete the loading. Close all valves of the reaction system, use a vacuum pump to evacuate the vacuum in the reaction tube to ≤1 Pa, and then introduce Ar (flow rate 50 mL·min). -1 Purge for 30 minutes to remove air and moisture from the system.

[0045] (6) The gas was switched to a 10% H2 / Ar mixture at a flow rate of 45 mL·min. -1 Turn on the full-spectrum LED light source and adjust the light intensity to 1.0 W·cm. -2 At the same time, at 2 ℃·min -1 The temperature was raised to 230 °C and maintained for 2 h to complete the in-situ photoreduction (during this process, CuO in the precursor was reduced to metallic Cu nanoparticles, which together with unreduced ZnO and highly dispersed Ga formed a Cu / ZnO / Ga heterogeneous interface active structure).

[0046] (7) After the reduction is complete, maintain a light intensity of 1.0 W·cm. -2 The temperature was raised to 240 °C, the 10% H2 / Ar flow was turned off, and the reaction gases were switched to CO2 and H2, with an H2:CO2 ratio of 3:1 and a reaction space velocity of 3600 h⁻¹. -1 Simultaneously, the system pressure is slowly increased to 3 MPa to start the reaction.

[0047] Example 3 (1) The molar ratio of copper to zinc is 3:2, and the mass ratio of CuO-ZnO composite oxide to Ga is 20:1.

[0048] Prepare 0.125 mol·L⁻¹ solutions respectively. -1A mixed salt solution was prepared by mixing 100 mL of Cu(NO3)2·6H2O solution with 66.7 mL of Zn(NO3)2·6H2O solution to form a mixed salt solution. The copper-zinc salt solution and the Na2CO3 solution were simultaneously added dropwise to a three-necked flask using a peristaltic pump, controlling the precipitation temperature at 70 °C and the precipitation pH at 7.0, resulting in mixed slurry A. After the addition was complete, the mixture was aged at 80 °C for 2 h to obtain a blue-green suspension.

[0049] (2) The suspension was vacuum filtered, and the filter cake was washed four times with deionized water. The filter cake was then transferred to a vacuum drying oven and dried at 100 °C for 10 h to obtain the catalyst precursor. The dried precursor was placed in a muffle furnace and calcined at 350 °C for 3 h in air atmosphere at a heating rate of 5 °C·min. -1 After natural cooling, it is ground into fine powder to obtain CuO-ZnO composite oxide (denoted as CZ).

[0050] (3) With a ball-to-powder ratio of 10:1, place 2 g of CZ powder, 0.1 g of Ga, and 21 g of grinding balls into a ball mill jar. Vacuum the ball mill jar through a valve, and then fill it with inert argon gas. Securely install the ball mill jar onto a planetary ball mill. Start the cooling system to ensure that the jar temperature is maintained below 25 °C (e.g., 25 °C) during the ball milling process to keep gallium in a solid state and ensure effective ball milling dispersion. Set the ball mill speed to 300 rpm and the ball milling time to 7 h.

[0051] (4) After the ball milling process is completed, wait for the ball mill jar to cool completely to room temperature before opening it. Pour the powder and grinding balls in the jar into a sieve to separate the powder product and obtain the CuO-ZnO-Ga composite precursor.

[0052] (5) Transfer 0.2 g of CuO-ZnO-Ga composite precursor to a quartz reaction tube, compact it, and place it in the photothermal reaction system to complete the loading. Close all valves of the reaction system, use a vacuum pump to evacuate the vacuum in the reaction tube to ≤1 Pa, and then introduce Ar (flow rate 50 mL·min). -1 Purge for 30 minutes to remove air and moisture from the system.

[0053] (6) The gas was switched to a 10% H2 / Ar mixture at a flow rate of 45 mL·min. -1 Turn on the full-spectrum LED light source and adjust the light intensity to 1.0 W·cm. -2 At the same time, at 2 ℃·min -1The temperature was raised to 230 °C and maintained for 2 h to complete the in-situ photoreduction (during this process, CuO in the precursor was reduced to metallic Cu nanoparticles, which together with unreduced ZnO and highly dispersed Ga formed a Cu / ZnO / Ga heterogeneous interface active structure).

[0054] (7) After the reduction is complete, maintain a light intensity of 1.0 W·cm. -2 The temperature was raised to 240 °C, the 10% H2 / Ar flow was turned off, and the reaction gases were switched to CO2 and H2, with an H2:CO2 ratio of 3:1 and a reaction space velocity of 3600 h⁻¹. -1 Simultaneously, the system pressure is slowly increased to 3 MPa to start the reaction.

[0055] Example 4 The difference from Example 1 is that in step (3), the mass ratio of CuO-ZnO composite oxide to Ga is 20:3, and 2 g of CZ powder, 0.3 g of Ga, and 23 g of grinding balls are placed together in a ball mill jar. Everything else is the same as in Example 1.

[0056] Example 5 The difference from Example 1 is that in step (3), the mass ratio of CuO-ZnO composite oxide to Ga is 20:5, and 2 g of CZ powder, 0.5 g of Ga, and 25 g of grinding balls are placed together in a ball mill jar. Everything else is the same as in Example 1.

[0057] Example 6 The difference from Example 1 is that the ball-to-material ratio in step (3) is 15:1, while the rest remains the same as in Example 1.

[0058] Example 7 The difference from Example 1 is that the ball-to-material ratio in step (3) is 20:1, while the rest is the same as in Example 1.

[0059] Example 8 The difference from Example 1 is that in step (6), the light intensity is adjusted to 3.0 W·cm. -2 Everything else remains the same as in Example 1.

[0060] Example 9 The difference from Example 1 is that the in-situ light restoration time in step (6) is 4 h.

[0061] Comparative Example 1 A one-step coprecipitation method was used to prepare Cu / ZnO / Al2O3 (Cu:Zn:Al=6:2:1) catalyst.

[0062] (1) Prepare 0.125 mol·L⁻¹ solutions respectively -1Cu(NO3)2·6H2O, Zn(NO3)2·6H2O, Al(NO3)3·9H2O, and sodium carbonate solution were prepared. Specifically, 100 mL of Cu(NO3)2·6H2O solution, 33.33 mL of Zn(NO3)2·6H2O solution, and 16.67 mL of Al(NO3)3·9H2O solution were mixed thoroughly in a beaker. This mixture, along with the sodium carbonate solution, was then added dropwise to a three-necked flask at 70 °C. The pH of the system was controlled at 7.0. After the addition was complete, the mixture was aged at 70 °C for 1 h. After aging, the resulting slurry was washed and filtered.

[0063] (2) Place the washed filter cake in an oven and dry it at 105 °C for 12 h, then place it in a muffle furnace and dry it at 5 °C·min. -1 The temperature was increased to 450 °C at a certain heating rate, and the mixture was calcined at a constant temperature for 4 h. After natural cooling to room temperature, the CuO / ZnO / Al2O3 catalyst was obtained.

[0064] (3) Transfer 0.2 g of CuO / ZnO / Al2O3 catalyst to a quartz reaction tube, compact it and place it in the reaction system to complete the filling.

[0065] (4) Introduce a 10% H2 / Ar mixture at a flow rate of 45 mL·min -1 , at 2 ℃·min -1 The temperature was raised to 230 °C and maintained for 2 h to complete the catalyst reduction.

[0066] (5) After the reduction is complete, the temperature is raised to 240 °C, the 10% H2 / Ar is turned off, and the reaction gases CO2 and H2 are switched to reactant gases, with H2:CO2=3:1 and the reaction space velocity is 3600 h. -1 Simultaneously, the system pressure is slowly increased to 3 MPa to start the reaction.

[0067] Comparative Example 2 (1) The molar ratio of copper and zinc components is 6:1, and the mass ratio of CuO-ZnO composite oxide to Ga is 20:1.

[0068] Prepare 0.125 mol·L⁻¹ solutions respectively. -1 A mixed salt solution was prepared by mixing 100 mL of Cu(NO3)2·6H2O solution, 16.67 mL of Zn(NO3)2·6H2O solution, and 16.67 mL of Na2CO3 solution. The copper-zinc salt solution and Na2CO3 solution were then simultaneously added dropwise to a three-necked flask using a peristaltic pump. The precipitation temperature was controlled at 70 °C, and the pH of the precipitation was 7.0, resulting in mixed slurry A. After the addition was complete, the mixture was aged at 80 °C for 2 h to obtain a blue-green suspension.

[0069] (2) The suspension was vacuum filtered, and the filter cake was washed four times with deionized water. The filter cake was then transferred to a vacuum drying oven and dried at 100 °C for 10 h to obtain the catalyst precursor. The dried precursor was placed in a muffle furnace and calcined at 350 °C for 3 h in air atmosphere at a heating rate of 5 °C·min. -1 After natural cooling, it is ground into fine powder to obtain CuO-ZnO composite oxide (denoted as CZ).

[0070] (3) With a ball-to-powder ratio of 10:1, place 2 g of CZ powder, 0.1 g of Ga, and 21 g of grinding balls into a ball mill jar. Vacuum the ball mill jar through a valve, and then fill it with inert argon gas. Securely install the ball mill jar onto a planetary ball mill. Start the cooling system to ensure that the jar temperature is maintained below 25 °C (e.g., 25 °C) during the ball milling process to keep gallium in a solid state and ensure effective ball milling dispersion. Set the ball mill speed to 300 rpm and the ball milling time to 7 h.

[0071] (4) After the ball milling process is completed, wait for the ball mill jar to cool completely to room temperature before opening it. Pour the powder and grinding balls in the jar into a sieve to separate the powder product and obtain the CuO-ZnO-Ga composite precursor.

[0072] (5) Transfer 0.2 g of CuO-ZnO-Ga composite precursor to a quartz reaction tube, compact it and place it in the reaction system to complete the filling.

[0073] (6) Introduce a 10% H2 / Ar mixture at a flow rate of 45 mL·min -1 , at 2 ℃·min -1 The temperature was raised to 230 °C and maintained for 2 h to complete the catalyst reduction (during this process, CuO in the precursor was reduced to metallic Cu nanoparticles, which together with unreduced ZnO and highly dispersed Ga formed a Cu / ZnO / Ga heterogeneous interfacial active structure).

[0074] (7) After the reduction is complete, the temperature is raised to 240 °C, the 10% H2 / Ar is turned off, and the reaction gases CO2 and H2 are switched to reactants with a ratio of H2:CO2 = 3:1 and a space velocity of 3600 h⁻¹. -1 Simultaneously, the system pressure is slowly increased to 3 MPa to start the reaction.

[0075] Comparative Example 3 (1) The molar ratio of copper to zinc is 6:1.

[0076] Prepare 0.125 mol·L⁻¹ solutions respectively. -1A mixed salt solution was prepared by mixing 100 mL of Cu(NO3)2·6H2O solution, 16.67 mL of Zn(NO3)2·6H2O solution, and 16.67 mL of Na2CO3 solution. The copper-zinc salt solution and Na2CO3 solution were then simultaneously added dropwise to a three-necked flask using a peristaltic pump. The precipitation temperature was controlled at 70 °C, and the pH of the precipitation was 7.0, resulting in mixed slurry A. After the addition was complete, the mixture was aged at 80 °C for 2 h to obtain a blue-green suspension.

[0077] (2) The suspension was vacuum filtered, and the filter cake was washed four times with deionized water. The filter cake was then transferred to a vacuum drying oven and dried at 100 °C for 10 h to obtain the catalyst precursor. The dried precursor was placed in a muffle furnace and calcined at 350 °C for 3 h in air atmosphere at a heating rate of 5 °C·min. -1 After natural cooling, it is ground into fine powder to obtain CuO-ZnO composite oxide.

[0078] (3) Transfer 0.2 g of Cu-ZnO catalyst to a quartz reaction tube, compact it, and place it in the photothermal reaction system to complete the loading. Close all valves of the reaction system, use a vacuum pump to evacuate the vacuum in the reaction tube to ≤1 Pa, and then introduce Ar (flow rate 50 mL·min). -1 Purge for 30 minutes to remove air and moisture from the system.

[0079] (4) The gas was switched to a 10% H2 / Ar mixture with a flow rate of 45 mL·min. -1 Turn on the full-spectrum LED light source and adjust the light intensity to 1.0 W·cm. -2 At the same time, at 2 ℃·min -1 The temperature was raised to 230 °C and maintained for 2 h to complete the in-situ photoreduction (reducing the CuO-ZnO composite oxide to a Cu / ZnO heterogeneous structure).

[0080] (5) After the reduction is complete, maintain a light intensity of 1.0 W·cm. -2 The temperature was raised to 240 °C, the 10% H2 / Ar flow was turned off, and the reaction gases were switched to CO2 and H2, with an H2:CO2 ratio of 3:1 and a reaction space velocity of 3600 h⁻¹. -1 Simultaneously, the system pressure is slowly increased to 3 MPa to start the reaction.

[0081] Effect test After the reaction is started, the product is sampled and analyzed using a gas chromatograph. The test time is the average value of 6 consecutive hours after the reaction stabilizes.

[0082] TCD detector (carrier gas He): detects the content of CO2, H2, and CO, and calculates the CO2 conversion rate; FID detector (carrier gas N2, 8% Ar as internal standard): detects methanol content and calculates methanol selectivity.

[0083] Methanol selectivity = (Number of C atoms in methanol) / (Number of C atoms in the converted CO2) × 100% A Cu-ZnO-Ga heterogeneous nanocatalyst was prepared using a phase engineering strategy, enabling efficient CO2 hydrogenation to methanol under photothermal synergistic conditions. The CO2 hydrogenation performance test results are listed in Table 1.

[0084] Table 1. CO2 hydrogenation performance on different catalysts

[0085] As shown in Table 1, the heterogeneous nanocatalysts in the embodiments of this application exhibit significantly higher methanol space-time yield, selectivity, and CO2 selectivity than the catalyst prepared by co-precipitation in Comparative Example 1, the catalyst without in-situ photoreduction in Comparative Example 2, and the catalyst without Ga in Comparative Example 3. The heterogeneous nanocatalysts demonstrate higher catalytic activity, methanol space-time yield, and selectivity.

[0086] The above data indicate that having both a CuO-ZnO-Ga precursor with a specific composition and a Cu / ZnO / Ga heterogeneous interface structure constructed through in-situ photoreduction is key to obtaining high catalytic performance.

[0087] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and changes to the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection of this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A heterogeneous nanocatalyst for the catalytic hydrogenation of CO2 to methanol, characterized in that, Its precursor contains CuO-ZnO composite oxide and Ga, with Ga distributed in a highly dispersed state therein; After reduction and activation, the precursor forms a heterogeneous interface structure containing metals Cu, ZnO and Ga; wherein the molar ratio of Cu to Zn is 3:(0.5~2) and the mass ratio of CuO-ZnO composite oxide to Ga is 20:(1~5).

2. The heterogeneous nanocatalyst according to claim 1, characterized in that, The molar ratio of Cu to Zn is 6:1, 5:2, or 3:

2.

3. The heterogeneous nanocatalyst according to claim 1, characterized in that, The mass ratio of the CuO-ZnO composite oxide to Ga is 20:1, 20:3, or 20:

5.

4. The method for preparing heterogeneous nanocatalysts according to any one of claims 1-3, characterized in that, include: CuO-ZnO composite oxides were prepared by co-precipitation method; The obtained CuO-ZnO composite oxide was physically ball-milled with metallic Ga to obtain the precursor of the heterogeneous nanocatalyst; wherein the metallic Ga was solidified before ball milling and remained solid during ball milling.

5. The method for preparing heterogeneous nanocatalysts according to claim 4, characterized in that, Cu 2+ and Zn 2+ A mixed salt solution and a precipitant were added dropwise to a reaction vessel in parallel flow. The precipitation temperature was controlled at 60-80 °C, and the final pH of the precipitation was 6.5-8.5, resulting in a precipitated slurry. The precipitated slurry was aged at 70-90 °C for 1-3 hours, and after solid-liquid separation, washing, and drying, it was calcined at 300-400 °C for 2-4 hours to obtain the CuO-ZnO composite oxide. Optionally, the physical ball milling is carried out under an inert atmosphere, with a ball-to-material ratio of (10~20):1, a ball milling speed of 300-500 rpm, a ball milling time of 5~10 hours, and a ball milling process temperature controlled below 25 ℃. Optionally, the ball-to-material ratio is 10:1, 15:1, or 20:

1.

6. The method for preparing heterogeneous nanocatalysts according to claim 4 or 5, characterized in that, It also includes in-situ photoreduction treatment of the precursor of the heterogeneous nanocatalyst; the method of in-situ photoreduction treatment is as follows: in a reducing atmosphere containing H2, under a light intensity of 1~3.0 W·cm -2 Under these conditions, the temperature is raised to 200-250 °C and maintained for 1-4 hours; preferably, the light intensity is 1.0 W·cm. -2 The reduction temperature was 230 ℃ and the reduction time was 2 hours.

7. A method for catalytic hydrogenation of CO2 to methanol using the heterogeneous nanocatalyst according to any one of claims 1-6, characterized in that, Under the influence of light, heating, and the catalyst that has undergone in-situ photoreduction treatment, a mixture of H2 and CO2 reaction gas is introduced to carry out a photothermal synergistic catalytic hydrogenation reaction to produce methanol.

8. The method for producing methanol by catalytic hydrogenation of CO2 according to claim 7, characterized in that, The conditions for the hydrogenation reaction are as follows: reaction temperature 220~260 ℃, reaction pressure 2~5 MPa, volume ratio of H2 to CO2 of the reaction gas (2~4):1, and space velocity 3600~5000 h⁻¹. -1 Preferably, the reaction temperature is 240 °C, the reaction pressure is 3 MPa, the volume ratio of H2 to CO2 in the reaction gases is 3:1, and the space velocity is 3600 h⁻¹. -1 .

9. The method for producing methanol by catalytic hydrogenation of CO2 according to claim 7, characterized in that, The light source is a full-spectrum LED light source with a light intensity of 0.5~3.0 W·cm. -2 Preferably, the light intensity is 1.0 W·cm. -2 .

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