A pd-cu bimetallic catalyst, a preparation method and application thereof

Abstract

This invention belongs to the field of hydrogenation catalyst technology, specifically relating to a Pd-Cu bimetallic catalyst, its preparation method, and its application. Using palladium nitrate and copper nitrate as metal sources, 2-methylimidazole as an organic ligand, and SiO2 as a support, a metal-organic framework precursor is constructed via a solvothermal method. This precursor is then subjected to a two-step heat treatment process: N2 atmosphere pyrolysis and air atmosphere calcination, yielding a PdxCu@SiO2 catalyst with an adjustable Pd / Cu molar ratio. The Cu loading is 4.0 wt.%, and the Pd loading is 0.5~5.5 wt.%. This invention features a mild and easily controllable process, allowing for precise optimization of the catalyst's active site structure. The SiO2 support effectively improves the catalyst's dispersibility and stability. The resulting catalyst exhibits excellent performance in CO2 hydrogenation to methanol, with a maximum CO2 conversion rate of 16.3%, a methanol selectivity of 64.5%, and a space-time yield approximately 18.5 times higher than that of the traditional impregnation method, while also demonstrating excellent long-term operational stability.

Description

Technical Field

[0001] This invention belongs to the field of hydrogenation catalyst technology, specifically relating to a Pd-Cu bimetallic catalyst, its preparation method, and its application. Background Technology

[0002] With the continued advancement of the global "dual carbon" strategic goals, the resource utilization of carbon dioxide (CO2) has become one of the core research directions in the fields of energy, chemical engineering, and environmental governance. Among them, the production of methanol through hydrogenation catalytic reaction using CO2 and "green hydrogen" (H2) obtained from renewable energy sources can achieve efficient CO2 fixation and carbon recycling, alleviating the ecological and environmental pressure caused by the greenhouse effect. It can also convert intermittent renewable energy into easily stored and transportable liquid fuels and basic chemical raw materials. It is currently the most promising carbon recycling technology with extremely high industrial application value.

[0003] The catalyst is the core of the CO2 hydrogenation to methanol reaction system, directly determining the CO2 conversion efficiency, the selectivity of the target product methanol, the production efficiency, and the long-term operational stability during the reaction. Based on the catalytically active component, the catalyst systems widely studied in this field mainly include four categories: copper (Cu)-based catalysts, noble metal (Pd, Au, etc.)-based catalysts, indium oxide (In2O3)-based catalysts, and solid solution catalysts such as ZnZrOx. Among these, Cu-based catalysts are the most widely studied and considered to have the greatest potential for industrial application due to their excellent CO2 catalytic conversion activity and low raw material cost.

[0004] However, single-metal catalysts still face significant technical bottlenecks in the CO2 hydrogenation to methanol reaction: Cu-based single-metal catalysts suffer from insufficient catalytic activity, easy sintering and deactivation of active components under high temperature and high pressure reaction conditions, and poor long-term cycle stability; although Pd-based single-metal catalysts have extremely strong dissociation and adsorption capabilities for H2, enabling H2 molecules to be efficiently decomposed into active hydrogen atoms and exhibiting excellent catalytic activity in hydrogenation reactions, it is difficult to achieve high selectivity control of the target product methanol when applied alone to the CO2 hydrogenation to methanol reaction.

[0005] Recent research shows that constructing bimetallic catalytic systems is an effective strategy to overcome the performance bottleneck of monometallic catalysts and improve methanol synthesis performance. Among them, the Pd-Cu bimetallic catalytic system has become a research focus in this field: the introduction of Pd can significantly improve the methanol synthesis performance of Cu / SiO2 catalysts, and the formation of Pd-Cu alloys can regulate the adsorption performance of catalysts for CO2 and H2, enhance the adsorption and activation capacity of reactants, and thus improve the catalytic performance of methanol synthesis. However, the preparation and application of Pd-Cu bimetallic catalysts still face many technical problems that need to be solved. Existing preparation methods are difficult to achieve highly dispersed and uniform loading of active components and cannot accurately construct Pd-Cu synergistic active sites, which leads to the catalyst being prone to reverse water-gas shift (RWGS) side reactions during the reaction, generating CO byproducts and significantly reducing methanol selectivity. At the same time, the interaction between the active components and the support is weak, and active nanoparticles are prone to migration, sintering, oxidation, and detachment during high-temperature and high-pressure reactions, causing rapid catalyst deactivation and making it difficult to meet the industrial requirements for long-term stable operation.

[0006] Currently, the mainstream preparation method for Pd-Cu bimetallic catalysts is the impregnation method. Although this method has a simple operation process, it has inherent drawbacks that cannot be overcome: Pd-Cu / SiO2 catalysts prepared by the impregnation method exhibit poor dispersion of the active components on the support surface, making it difficult to form a uniformly coupled Pd-Cu active dual interface, thus failing to fully realize the synergistic effect of the Pd-Cu bimetallic catalyst; simultaneously, the strong metal-support interaction is weak, failing to effectively suppress the migration and sintering of active components and the occurrence of side reactions. According to existing catalytic performance data, in the CO2 hydrogenation to methanol reaction, the Pd-Cu / SiO2 catalyst prepared by the impregnation method exhibits a maximum CO2 conversion of only 6.9%, a maximum methanol selectivity of only 34.5%, and a maximum methanol space-time yield of only 0.103 g·gcat. -1 ·h -1 The catalytic activity, product selectivity, and production efficiency are all difficult to meet the requirements for industrial application.

[0007] In-situ growth, as a novel catalyst preparation technology, possesses core advantages such as strong interfacial bonding between the active component and the support, resistance to detachment, peeling, or failure, uniform growth across the entire substrate, precise controllable growth conditions, no need for complex vacuum equipment, simple preparation process, and ease of large-scale production. It provides a new approach to address the shortcomings of existing Pd-Cu bimetallic catalyst technologies. However, current in-situ growth methods for Pd-Cu bimetallic catalysts used in CO2 hydrogenation to methanol still cannot achieve precise control of the Pd / Cu molar ratio through simple and mild process conditions. This makes it difficult to simultaneously optimize the active site structure, active component dispersion, and operational stability of the catalyst, and cannot simultaneously achieve high catalytic activity, high methanol selectivity, high space-time yield, and excellent long-term cycling stability in the CO2 hydrogenation to methanol reaction. Therefore, developing a Pd-Cu bimetallic catalyst preparation method with mild process conditions, easy process control, scalable production, and the ability to simultaneously achieve high CO2 conversion, high methanol selectivity, high space-time yield, and excellent operational stability is a pressing technical problem to be solved in this field. Summary of the Invention

[0008] The purpose of this invention is to provide a Pd-Cu bimetallic catalyst, its preparation method, and its application. The active site structure of the catalyst can be precisely optimized by adjusting the molar ratio of Pd to Cu, adapting to different catalytic reaction conditions and providing a new approach to the structural design of efficient hydrogenation catalysts.

[0009] The objective of this invention is achieved through the following technical solution: This invention provides a Pd-Cu bimetallic catalyst, wherein the catalyst has a PdxCu@SiO2 structure, with SiO2 as the support and Pd-Cu bimetallic active components supported in situ; based on the total mass of the catalyst, the loading of Cu is 4.0 wt.%, the loading of Pd is 0.5~5.5 wt.%, and x is the molar ratio of Pd to Cu, with x taking values ​​of 0.5, 0.33, 0.2, 0.1 or less than 0.1.

[0010] Furthermore, x is 0.33, and the Pd loading is 2.17 wt.% based on the total mass of the catalyst.

[0011] This invention also provides a method for preparing Pd-Cu bimetallic catalysts by in-situ growth, comprising the following steps: 1) Copper nitrate, palladium nitrate, and 2-methylimidazole were dissolved in ethanol solvent to prepare solutions A, B, and C respectively; 2) Add solutions A, B, and C sequentially to a container containing SiO2 support, and then subject the solutions to ultrasonication, stirring, and settling to obtain a precipitate. 3) The obtained precipitate was washed with ethanol and then dried to obtain the catalyst precursor; 4) The catalyst precursor is first subjected to pyrolysis under a nitrogen atmosphere, and then calcined under an air atmosphere to obtain a Pd-Cu bimetallic catalyst.

[0012] Furthermore, in step 1), the total molar amount of copper nitrate and palladium nitrate metal ions is in a molar ratio of 1:4 to 2-methylimidazole.

[0013] Furthermore, in step 2), the ultrasonic treatment time is 5 minutes, the stirring treatment is reflux stirring in an 80°C oil bath for 6 hours, and the settling treatment is settling and aging at room temperature for 60 hours.

[0014] Furthermore, in step 3), the drying temperature is 60-100℃ and the drying time is 12h.

[0015] Furthermore, in step 4), the pyrolysis treatment is carried out in a tubular atmosphere furnace at a pyrolysis temperature of 500°C, a pyrolysis time of 4 hours, and a heating rate of 5°C / min.

[0016] Furthermore, in step 4), the calcination treatment is carried out in a muffle furnace at a calcination temperature of 400°C for 2 hours and a heating rate of 5°C / min.

[0017] This invention also provides an application of a Pd-Cu bimetallic catalyst in the reaction of carbon dioxide hydrogenation to methanol, wherein the Pd-Cu bimetallic catalyst is the Pd-Cu bimetallic catalyst described above, or a Pd-Cu bimetallic catalyst prepared by the method described above.

[0018] Furthermore, the process conditions for the carbon dioxide hydrogenation to methanol reaction are as follows: reaction temperature 250℃, molar ratio of CO2 to H2 in the reactants 1:3, reaction pressure 4.0 MPa, and reaction space velocity 3600 mL·gcat. -1 ·h -1 .

[0019] The beneficial effects of this invention are as follows: The Pd-Cu bimetallic catalyst provided by this invention is prepared by in-situ growth, with mild overall preparation conditions, easily controllable process parameters, no need for complex vacuum preparation equipment, and a simple and convenient operation process, meeting the relevant requirements of green chemistry and possessing good potential for large-scale production. This method uses palladium nitrate and copper nitrate as metal sources, 2-methylimidazole as organic ligand, and SiO2 as support. First, a metal-organic framework precursor is constructed via a solvothermal method, followed by two-step heat treatment: nitrogen atmosphere pyrolysis and air atmosphere calcination. This yields PdxCu@SiO2 catalysts with different Pd / Cu molar ratios. The Pd to Cu molar ratio x can be set to 0.5, 0.33, 0.2, 0.1, or less than 0.1, corresponding to a fixed Cu loading of 4.0 wt.% and a Pd loading that can be flexibly adjusted within the range of 0.5~5.5 wt.%. By adjusting the Pd to Cu molar ratio, the active site structure of the catalyst can be precisely optimized to adapt to different catalytic reaction conditions, providing a new approach for the structural design of high-efficiency hydrogenation catalysts.

[0020] The in-situ growth method employed in this invention enables a strong interfacial bond between the active component and the SiO2 support, effectively preventing the active component from detaching, peeling, or failing during use. Furthermore, the growth process can be carried out uniformly on the SiO2 support substrate, allowing for precise control of the active component's growth state. The introduction of the SiO2 support effectively improves the dispersibility of the active component. Combined with the strong metal-support interaction formed by in-situ growth, it prevents the migration, sintering, and oxidation of Pd-Cu nanoparticles in the high-temperature, high-pressure reaction environment, fundamentally improving the defects of traditional catalysts that are prone to sintering and deactivation. Simultaneously, achieving in-situ growth of the active component on a three-dimensional support also effectively improves mass transfer and heat dissipation during the catalytic reaction, enhancing the overall reaction efficiency.

[0021] This invention constructs a uniform, highly dispersed, and tightly coupled Pd-Cu active dual interface through in-situ growth, fully leveraging the synergistic effect of the bimetallic components. The formation of the Pd-Cu alloy helps optimize the adsorption performance of the reactants. Simultaneously, the Pd base sites possess extremely strong dissociation and adsorption capabilities for H2, enabling H2 molecules to efficiently decompose into active hydrogen atoms, which then rapidly overflow and migrate to adjacent Cu sites that possess strong chemisorption and activation capabilities for CO2 molecules. Based on catalytic performance test results, it is speculated that the reaction process of this catalyst tends to follow a more efficient formate reaction pathway, effectively suppressing the occurrence of reverse water-gas shift side reactions. This solves the core problems of insufficient activity and poor selectivity of target products in traditional single-metal catalysts.

[0022] The series of PdxCu@SiO2 catalysts prepared in this invention all achieved significant improvements in CO2 conversion, methanol selectivity, and methanol space-time yield in the carbon dioxide hydrogenation to methanol reaction, with overall catalytic performance far superior to that of Pd-Cu catalysts with the same proportions prepared by the traditional impregnation method. Among them, the Pd0.33Cu@SiO2 catalyst exhibited the best catalytic performance at a reaction temperature of 250℃, a molar ratio of CO2 to H2 of 1:3, a reaction pressure of 4.0 MPa, and a reaction space velocity of 3600 mL·gcat. -1 ·h -1 Under these conditions, the CO2 conversion rate reached 16.3%, the methanol selectivity reached 64.5%, and the methanol space-time yield reached 2.03 g·gcat. -1 ·h -1 Compared to the best catalyst prepared by the impregnation method, the performance is improved by about 18.5 times, and the improvement in catalytic performance is extremely significant.

[0023] The Pd-Cu bimetallic catalyst prepared in this invention exhibits excellent operational stability during long-term use, maintaining stable catalytic performance without significant activity decay even after 150 hours of long-term catalytic testing. Furthermore, this catalyst is suitable for the mainstream reaction process of carbon dioxide hydrogenation to methanol, demonstrating excellent catalytic activity, target product selectivity, and cycle stability in the catalytic hydrogenation reaction. It provides high-performance catalytic material support for the industrial application of carbon dioxide resource recycling, possessing promising industrial application prospects and practical value. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The image shows the XRD pattern of the calcined PdxCu / @SiO2 catalyst of this invention. Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0029] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0030] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0031] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0032] The Pd-Cu bimetallic catalyst provided by this invention is a PdxCu@SiO2 catalyst prepared by in-situ growth method, wherein x is the molar ratio of Pd to Cu, and the value of x is 0.5, 0.33, 0.2, 0.1 or <0.1; in the catalyst, the fixed loading of Cu is 4.0 wt.%, and the loading of Pd is 0.5~5.5 wt.%.

[0033] General methods for catalyst preparation The Pd-Cu bimetallic catalyst of this invention is prepared by in-situ growth method, and the general preparation steps are as follows: Solution preparation: Dissolve copper nitrate in 25 mL of anhydrous ethanol and stir until completely dissolved to form solution A; dissolve palladium nitrate in 25 mL of anhydrous ethanol and stir until completely dissolved to form solution B; dissolve 2-methylimidazole in 25 mL of anhydrous ethanol and stir until completely dissolved to form solution C; wherein, the total metal ions in the system (Cu) 2+ +Pd 2+ The molar ratio of 1 to 2-methylimidazole is 1:4.

[0034] In-situ growth and precursor preparation: Weigh 1g of SiO2 support and place it in a reaction vessel. Add the above solutions A, B and C sequentially to the reaction vessel containing the SiO2 support. First, sonicate for 5min to ensure that each component is fully mixed with the support. Then place it in an oil bath and reflux vigorously at 80℃ for 6h. After stirring, let it stand at room temperature for 60h to obtain the precipitate.

[0035] Washing and drying: The precipitate obtained in step 2 was washed multiple times with anhydrous ethanol. After washing, it was placed in a forced-air drying oven and dried at 60~100℃ for 12h to obtain the catalyst precursor.

[0036] Heat treatment: The catalyst precursor obtained in step 3 was placed in a tube furnace and pyrolyzed at 500℃ for 4 hours in N2 atmosphere with a heating rate of 5℃ / min. After pyrolysis, the material was placed in a muffle furnace and calcined at 400℃ in air atmosphere for 2 hours with a heating rate of 5℃ / min to remove the organic framework structure and finally obtain the PdxCu@SiO2 bimetallic catalyst.

[0037] Example 1 This embodiment prepares a Pd0.5Cu@SiO2 bimetallic catalyst with a Pd / Cu molar ratio of x=0.5. The specific preparation steps are as follows: Solution preparation: Weigh 0.293g of copper nitrate into beaker 1, add 25mL of anhydrous ethanol, and stir until completely dissolved to form solution A; weigh 0.18g of palladium nitrate into beaker 2, add 25mL of anhydrous ethanol, and stir until completely dissolved to form solution B; weigh 0.77g of 2-methylimidazole into beaker 3, add 25mL of anhydrous ethanol, and stir until completely dissolved to form solution C; wherein, the molar ratio of total metal ions to 2-methylimidazole in the system is 1:4.

[0038] In-situ growth and precursor preparation: Weigh 1g of SiO2 support and place it in beaker 4. Add the above solutions A, B and C to beaker 4 in sequence. First, sonicate for 5min to ensure that each component is fully mixed with the support. Then place it in an oil bath and reflux vigorously at 80℃ for 6h. After stirring, let it stand at room temperature for 60h to obtain the precipitate.

[0039] Washing and drying: The obtained precipitate was washed multiple times with anhydrous ethanol. After washing, it was transferred to a forced-air drying oven and dried at 80°C for 12 hours to obtain the catalyst precursor.

[0040] Heat treatment: The obtained catalyst precursor was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under N2 atmosphere, and held for 4h for pyrolysis; after pyrolysis, the material was placed in a muffle furnace and heated to 400℃ at a heating rate of 5℃ / min under air atmosphere, and held for calcination for 2h. After natural cooling, a Pd0.5Cu@SiO2 bimetallic catalyst with Pd loading of 5.3wt.% and Cu loading of 4.0wt.% was obtained.

[0041] Example 2 In this embodiment, a Pd0.33Cu@SiO2 bimetallic catalyst was prepared with a Pd / Cu molar ratio of x=0.33. The specific preparation steps are as follows: the amount of palladium nitrate was adjusted so that the Pd loading in the catalyst was 3.92 wt.% and the Cu loading was fixed at 4.0 wt.%; the other raw material types, feeding ratios (the molar ratio of total metal ions to 2-methylimidazole was still 1:4), preparation steps, and process parameters were completely consistent with those in Example 1, and the Pd0.33Cu@SiO2 bimetallic catalyst was finally obtained.

[0042] Example 3 In this embodiment, a Pd0.2Cu@SiO2 bimetallic catalyst was prepared with a Pd / Cu molar ratio of x=0.2. The specific preparation steps are as follows: the amount of palladium nitrate was adjusted so that the Pd loading in the obtained catalyst was 2.17 wt.% and the Cu loading was fixed at 4.0 wt.%; the other raw material types, feeding ratios (the molar ratio of total metal ions to 2-methylimidazole was still 1:4), preparation steps, and process parameters were completely consistent with those in Example 1, and the Pd0.2Cu@SiO2 bimetallic catalyst was finally obtained.

[0043] Example 4 In this embodiment, a Pd0.1Cu@SiO2 bimetallic catalyst was prepared with a Pd / Cu molar ratio of x=0.1. The specific preparation steps are as follows: the amount of palladium nitrate was adjusted so that the Pd loading in the catalyst was 1.45 wt.% and the Cu loading was fixed at 4.0 wt.%. The other raw material types, feeding ratios (the molar ratio of total metal ions to 2-methylimidazole was still 1:4), preparation steps, and process parameters were completely consistent with those in Example 1, and the Pd0.1Cu@SiO2 bimetallic catalyst was finally obtained.

[0044] Example 5 This embodiment prepares a Pd<0.1Cu@SiO2 bimetallic catalyst with a Pd / Cu molar ratio x<0.1. The specific preparation steps are as follows: the amount of palladium nitrate is adjusted so that the Pd loading in the obtained catalyst is 0.91 wt.% and the Cu loading is fixed at 4.0 wt.%; the other raw material types, feeding ratios (the molar ratio of total metal ions to 2-methylimidazole is still 1:4), preparation steps, and process parameters are completely consistent with those in Example 1, and finally a Pd<0.1Cu@SiO2 bimetallic catalyst is obtained.

[0045] Comparative Example 1 This comparative example uses the traditional impregnation method to prepare PdxCu / SiO2 catalysts. Three groups of catalysts with Pd / Cu molar ratios x=0.5, 0.33, and 0.2 were prepared, respectively denoted as Pd0.5Cu / SiO2, Pd0.33Cu / SiO2, and Pd0.2Cu / SiO2. The specific preparation steps are as follows: According to the target Pd and Cu loading, the corresponding masses of copper nitrate and palladium nitrate were weighed and dissolved in deionized water to prepare a mixed impregnation solution; 1g of SiO2 support was weighed and added to the above mixed impregnation solution, and the mixture was stirred and impregnated at room temperature for 12h, followed by drying in an oven at 100℃ for 12h; after drying, the material was placed in a muffle furnace and calcined at 400℃ for 2h in an air atmosphere with a heating rate of 5℃ / min. After natural cooling, the corresponding impregnation method Pd-Cu bimetallic catalysts were obtained.

[0046] Experimental Example 1 2. Catalytic performance testing conditions The in-situ grown PdxCu@SiO2 catalysts prepared in Examples 1-5 above, and the impregnated PdxCu / SiO2 catalysts prepared in the comparative example, were respectively applied to the carbon dioxide hydrogenation to methanol reaction. The catalytic performance testing conditions for all catalysts were completely consistent, specifically: reaction temperature T = 250℃, CO2 / H2 molar ratio of reactant gas = 1 / 3, reaction pressure = 4.0 MPa, and volume hourly space velocity (VHSV) = 3600 mL·gcat. -1 ·h -1 .

[0047] 2. Catalytic performance test results The CO2 conversion rate, product selectivity, and methanol space-time yield of each catalyst group are shown in Table 1.

[0048] Table 1. Comparison of catalytic performance of a series of catalysts prepared by impregnation method and in-situ growth method

[0049] 3. Performance Comparison and Stability Test Results As shown in Table 1, compared with catalysts prepared by the traditional impregnation method, the PdxCu@SiO2 catalyst prepared by the in-situ growth method of this invention achieves significant improvements in CO2 conversion, methanol selectivity, and methanol space-time yield. Among them, the Pd0.33Cu@SiO2 catalyst prepared in Example 2 exhibits the best catalytic performance, achieving a CO2 conversion of 16.3%, a methanol selectivity of 64.5%, and a methanol space-time yield of 2.028 g·gcat under the aforementioned test conditions. -1 ·h -1 Compared to the best catalyst in the impregnation method (Pd0.2Cu / SiO2), the methanol space-time yield is increased by about 18.5 times.

[0050] Meanwhile, the optimal Pd0.33Cu@SiO2 catalyst was subjected to a long-term continuous reaction test for 150 hours. The test results showed that the catalyst did not show a significant decrease in catalytic activity and methanol selectivity during the 150-hour long-term operation, demonstrating excellent cycle stability and operational reliability.

[0051] 4. Catalyst structural characterization X-ray diffraction (XRD) was performed on the calcined PdxCu@SiO2 catalyst prepared in the embodiments of the present invention. The test patterns are shown below. Figure 1 As shown in the figure, the XRD results show that the catalyst prepared in this invention successfully achieved the loading and crystal formation of Pd-Cu bimetal on SiO2 support, and the active components were well dispersed on the support.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A Pd-Cu bimetallic catalyst, characterized in that, The catalyst has a PdxCu@SiO2 structure, with SiO2 as the support and Pd-Cu bimetallic active components loaded in situ. Based on the total mass of the catalyst, the loading of Cu is 4.0 wt.%, the loading of Pd is 0.5~5.5 wt.%, and x is the molar ratio of Pd to Cu, with values ​​of 0.5, 0.33, 0.2, 0.1 or less than 0.

1.

2. The Pd-Cu bimetallic catalyst according to claim 1, characterized in that, The x value is 0.33, and the Pd loading is 2.17 wt.% based on the total mass of the catalyst.

3. A method for preparing Pd-Cu bimetallic catalysts by in-situ growth, characterized in that, Includes the following steps: 1) Copper nitrate, palladium nitrate, and 2-methylimidazole were dissolved in ethanol solvent to prepare solutions A, B, and C respectively; 2) Add solutions A, B, and C sequentially to a container containing SiO2 support, and then subject the solutions to ultrasonication, stirring, and settling to obtain a precipitate. 3) The obtained precipitate was washed with ethanol and then dried to obtain the catalyst precursor; 4) The catalyst precursor is first subjected to pyrolysis under a nitrogen atmosphere, and then calcined under an air atmosphere to obtain a Pd-Cu bimetallic catalyst.

4. The preparation method according to claim 3, characterized in that, In step 1), the total molar amount of copper nitrate and palladium nitrate metal ions is in a molar ratio of 1:4 to 2-methylimidazole.

5. The preparation method according to claim 3, characterized in that, In step 2), the ultrasonic treatment time is 5 minutes, the stirring treatment is reflux stirring in an 80°C oil bath for 6 hours, and the static treatment is static aging at room temperature for 60 hours.

6. The preparation method according to claim 3, characterized in that, In step 3), the drying temperature is 60-100℃ and the drying time is 12h.

7. The preparation method according to claim 3, characterized in that, In step 4), the pyrolysis treatment is carried out in a tubular atmosphere furnace at a pyrolysis temperature of 500°C, a pyrolysis time of 4 hours, and a heating rate of 5°C / min.

8. The preparation method according to claim 3, characterized in that, In step 4), the calcination process is carried out in a muffle furnace at a temperature of 400°C for 2 hours and a heating rate of 5°C / min.

9. The application of a Pd-Cu bimetallic catalyst in the hydrogenation of carbon dioxide to methanol, characterized in that, The Pd-Cu bimetallic catalyst is the Pd-Cu bimetallic catalyst according to any one of claims 1-2, or the Pd-Cu bimetallic catalyst prepared by the preparation method according to any one of claims 2-8.

10. The application according to claim 9, characterized in that, The process conditions for the carbon dioxide hydrogenation to methanol reaction are as follows: reaction temperature 250℃, molar ratio of CO2 to H2 in the reactants 1:3, reaction pressure 4.0 MPa, and reaction space velocity 3600 mL·gcat. -1 ·h -1 .

Images