Cu-Fe-based catalyst as well as preparation method and application thereof

Abstract

The invention discloses a Cu-Fe-based catalyst as well as a preparation method and application thereof, relates to the technical field of catalysts, and solves the problems that an existing single-component Cu-based catalyst is low in methanol selectivity and a multi-metal composite catalyst is complex in synthetic route. The preparation method comprises the following steps: dropwise adding a NaOH solution into a La (NO3) 3.6 H2O solution, reacting the obtained turbid liquid in a hydrothermal reaction kettle to obtain a La (OH) 3 precursor, and washing, drying and annealing the La (OH) 3 precursor to obtain a hexagonal phase La2O2CO3 carrier; the hexagonal phase La2O2CO3 carrier is wetted with water, a ferric nitrate solution and a copper nitrate solution are dropwise added into the hexagonal phase La2O2CO3 carrier, annealing is carried out after a solvent is evaporated to dryness, and the Cu-Fe / La2O2CO3 catalyst is obtained. The Cu-Fe / La2O2CO3 catalyst prepared by the invention has excellent catalytic performance and methanol selectivity, and can be applied to a reaction for preparing methanol through CO2 hydrogenation.

Description

Technical Field

[0001] The present invention relates to the field of catalysts, and specifically relates to a Cu-Fe-based catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] With the global emphasis on environmental protection and sustainable development, the hydrogenation of CO2 to methanol has become an effective way to realize the resource utilization of CO2, which can not only reduce greenhouse gas emissions but also obtain high-value-added chemicals and liquid fuels. At present, various catalyst systems have been developed for the reaction of hydrogenating CO2 to methanol, such as copper-based catalysts, zinc-based catalysts, and supported catalysts. Among them, copper-based catalysts have been widely studied due to their low cost. However, in a catalyst system with a single-component Cu loading, due to the single Cu active center, side reactions are likely to occur during the hydrogenation of CO2, resulting in low methanol selectivity and making it difficult to achieve efficient conversion and production. Therefore, the development of multi-metal composite catalysts to improve the problem of low methanol selectivity of single Cu-based catalysts, and by regulating the synergistic effect between different metals, optimizing the electronic structure and geometric configuration of active sites, lays a foundation for promoting the development of methanol synthesis technology to a higher level.

[0003] At present, some researchers have provided metal composite Cu-based catalysts. For example, Chinese Patent Document CN114920623A provides a preparation method of a nickel-cerium composite material and its application in the reaction of hydrogenating CO2 to CO. Copper nitrate, zinc nitrate, and aluminum nitrate are dissolved in water and precipitated using anhydrous sodium carbonate to prepare a Cu / ZnO / Al2O3 precursor material, which is then subjected to silanization modification treatment and calcination to prepare the catalyst. This catalyst can significantly reduce the selectivity of by-product CO to less than 2 mol%, and exhibits excellent high-temperature stability and anti-sintering ability; however, the preparation cycle of this catalyst is long, and it requires repeated washing and drying, which is not suitable for large-scale industrial applications. Chinese Patent Document CN114130398A discloses a catalyst for hydrogenating CO2 to methanol and a preparation method thereof, mainly providing a preparation method and application of a Cu-based coordination polymer-derived catalyst for hydrogenating CO2 to methanol. The methanol space-time yield of the Cu / ZnO / ZrO2 catalytic material prepared using this derivative is 1.4 times that of the Cu / ZnO / ZrO2 catalyst prepared by the impregnation method, and it has good stability; however, the synthesis route of this catalyst is complex, and it requires the addition of a template agent harmful to the environment, which does not meet the requirements for environmental protection and promoting the sustainable development industry in the industrial reaction of hydrogenating CO2 to methanol.

[0004] Therefore, the current catalyst system for the reaction of hydrogenating CO2 to methanol has problems such as low methanol selectivity, high toxicity of some catalysts or coordination monomers, and complex synthesis routes. There is an urgent need to develop new catalysts and their preparation methods to achieve the efficient, green, and sustainable development of the reaction of hydrogenating CO2 to methanol. Summary of the Invention

[0005] To solve the problems of low methanol selectivity of existing single-component Cu-based catalysts and complex synthesis routes of multi-metal composite catalysts, the present invention proposes a Cu-Fe-based catalyst, its preparation method and application. The technical solution of the present invention is as follows:

[0006] A preparation method of a Cu-Fe-based catalyst, comprising the following preparation steps:

[0007] Dropwise add a NaOH solution to a La(NO3)3·6H2O solution, react the obtained suspension in a hydrothermal reaction kettle to obtain a La(OH)3 precursor, wash, dry and anneal the La(OH)3 precursor to obtain a hexagonal La2O2CO3 support; moisten the hexagonal La2O2CO3 support with water, dropwise add an iron nitrate solution and a copper nitrate solution thereto, evaporate the solvent and then anneal to obtain a Cu-Fe / La2O2CO3 catalyst;

[0008] Further, the molar ratio of La(NO3)3·6H2O to NaOH is 1:3.57 - 71.4; the molar ratio of the hexagonal La2O2CO3 support, iron nitrate and copper nitrate is 1:0.0127:0.0146;

[0009] Further, the temperature of the reaction is 160 °C and the reaction time is 12 h;

[0010] Further, the washing is carried out until the pH of the La(OH)3 precursor is 7;

[0011] Further, the temperature of the drying is 80 °C;

[0012] Further, the atmosphere of the first annealing is air, the annealing temperature is 550 °C, and the annealing time is 2 h;

[0013] Further, the temperature for evaporating the solvent is 80 °C;

[0014] Further, the atmosphere of the second annealing is hydrogen, the annealing temperature is 500 °C, and the annealing time is 2 h;

[0015] Further, the heating rate of both annealings is 10 °C / min.

[0016] A Cu-Fe-based catalyst prepared by the above method.

[0017] An application of the above Cu-Fe-based catalyst in the reaction of hydrogenating CO2 to methanol.

[0018] Compared with the prior art, the present invention solves the problems of low methanol selectivity of the existing single-component Cu-based catalyst and the complex synthesis route of the multi-metal composite catalyst. The specific beneficial effects are as follows:

[0019] 1. The Cu-Fe / La2O2CO3 catalyst provided by the present invention forms a CuFe alloy by the synergistic effect of Cu-Fe bimetals. The introduction of Fe effectively optimizes the electronic configuration of Cu species, enhances the adsorption capacity for methoxy intermediates (key intermediates in methanol formation), improves the stability of key intermediates in the reaction path, and thus improves the selectivity of methanol. The methanol selectivity of the Cu-Fe / La2O2CO3 catalyst can reach 60% at 260 °C, overcoming the problem that traditional Cu-based catalysts are prone to form by-products (such as CO and by-carbon hydrocarbons) in the reaction of CO2 hydrogenation to methanol.

[0020] 2. The La2O2 2+ groups on the surface of the hexagonal La2O2CO3 support prepared by the present invention have strong alkalinity and can promote CO2 adsorption. At the same time, the unique intercalated structure CO3 2- -La2O2 2+ of the hexagonal La2O2CO3 allows the exchange of CO2 molecules and H2O molecules on its surface, further enhancing the catalytic efficiency of the Cu-Fe / La2O2CO3 catalyst and laying a foundation for the excellent catalytic performance of the Cu-Fe / La2O2CO3 catalyst in the reaction of CO2 hydrogenation to methanol.

[0021] 3. The raw materials used to prepare the Cu-Fe / La2O2CO3 catalyst of the present invention are lanthanum nitrate, copper nitrate and iron nitrate. The raw materials are widely sourced and low in cost; the preparation process of the Cu-Fe / La2O2CO3 catalyst is simple and fast, easy to recycle and reuse, and can achieve large-scale industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the preparation flow chart of the Cu-Fe / La2O2CO3 catalyst;

[0023] Figure 2 is the X-ray diffraction pattern of the catalysts prepared in Examples 1-3;

[0024] Figure 3 is the transmission electron microscope image of the catalysts prepared in Examples 1-3 and the La2O2CO3 support;

[0025] Figure 4 is the CO2 conversion rate and methanol selectivity diagram of the catalysts prepared in Examples 1-3;

[0026] Figure 5 is the property diagram of methanol production by CO2 hydrogenation of the catalysts prepared in Examples 1-3. Detailed implementation mode

[0027] To make the technical solution of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as a limitation of the present invention.

[0028] Example 1.

[0029] Dissolve 2 g of La(NO3)3·6H2O in 50 mL of water, stir for 10 min, and dropwise add 6 mL of 10% wt NaOH solution thereto; transfer the obtained suspension to a hydrothermal reaction kettle and react at 160 °C for 12 h to obtain a La(OH)3 precursor, wash it until the pH of the precursor is 7, and dry it at 80 °C; then anneal the precursor in an air atmosphere at 550 °C to prepare a hexagonal La2O2CO3 support; transfer 250 mg of the La2O2CO3 support to a beaker, moisten the hexagonal La2O2CO3 support with 20 mL of water, dropwise add 687 μL of 0.1 mol / L iron nitrate solution and 790 μL of 0.1 mol / L copper nitrate solution thereto, and evaporate the solvent at 80 °C; take out the sample, anneal the sample in a 10% H2 atmosphere at 500 °C for 2 h with a heating rate of 10 °C / min to prepare a Cu-Fe / La2O2CO3 catalyst. As Figure 1 It is the preparation flow chart of the Cu-Fe / La2O2CO3 catalyst.

[0030] Catalytic hydrogenation of CO2 to methanol reaction:

[0031] Place 20 mg of the Cu-Fe / La2O2CO3 catalyst in a 40 cm long quartz tube reactor, fill the upper and lower parts of the quartz tube reactor with quartz wool, the reaction gas composition is 24% CO2 / 72% H2 / 4% Ar, the heating rate is 10 °C / min, the collected temperatures are: 200, 220, 240, 260, 280, 300 °C, and the reaction pressure is 3 MPa to realize the catalytic hydrogenation of CO2 to methanol reaction by the Cu-Fe / La2O2CO3 catalyst.

[0032] Example 2.

[0033] The difference between this example and Example 1 is that 1580 μL of 0.1 mol / L copper nitrate is added dropwise to the moistened hexagonal La2O2CO3 support, and iron nitrate is not added; the remaining preparation steps and conditions are the same as those in Example 1 to prepare a 2Cu / La2O2CO3 catalyst.

[0034] Example 3.

[0035] The difference between this example and Example 1 is as follows: 1374 μL of 0.1 mol / L iron nitrate was added dropwise to the wetted hexagonal La2O2CO3 support, and copper nitrate was not added; the remaining preparation steps and conditions were the same as those in Example 1, and the 2Fe / La2O2CO3 catalyst was prepared.

[0036] As Figure 2 Figure 1 is the X-ray diffraction pattern of the Cu-Fe / La2O2CO3, 2Cu / La2O2CO3 and 2Fe / La2O2CO3 catalysts. It can be seen from the figure that compared with the 2Cu / La2O2CO3 catalyst and the 2Fe / La2O2CO3 catalyst, the Cu-Fe / La2O2CO3 catalyst has higher crystallinity, which proves that the internal grain arrangement is more orderly, helps to reduce the defect centers, improve the catalytic activity, and overcomes the defect of low catalytic activity of the single-metal-loaded La2O2CO3 catalyst. As Figure 3 Figure 2 is the transmission electron micrograph of the Cu-Fe / La2O2CO3, 2Cu / La2O2CO3 and 2Fe / La2O2CO3 catalysts and the La2O2CO3 support. It can be seen from the figure that the La2O2CO3 support presents a nanorod-like structure and there is particle agglomeration; while the grain boundaries of the 2Fe / La2O2CO3 catalyst are blurred, indicating that Fe may exacerbate the agglomeration; compared with the La2O2CO3 support, the 2Cu-La2O2CO3 catalyst shows a certain degree of dispersion, but there is still a certain degree of agglomeration in some regions; the Cu-Fe / La2O2CO3 catalyst presents a more dispersed and uniform structure. This morphological change is due to the synergistic doping of Fe and Cu regulating the crystal growth process, suppressing the excessive aggregation of particles.

[0037] As Figure 4CO2 conversion and methanol selectivity diagrams for Cu-Fe / La2O2CO3, 2Cu / La2O2CO3, and 2Fe / La2O2CO3 catalysts; as can be seen from the figure, as the collection temperature increases, the CO2 conversion of the three catalysts shows an upward trend. This is because as the temperature increases, the active sites on the catalyst surface can more effectively promote the dissociation of CO2 and the activation of hydroxides, thereby increasing the CO2 conversion. However, as the temperature increases, the methanol selectivity of the 2Cu-La2O2CO3 and Cu-Fe / La2O2CO3 catalysts shows a decreasing trend. This is because the hydrogenation of CO2 to methanol is an exothermic reaction thermodynamically, and the reaction is favorable at low temperatures. However, it is difficult to activate stable CO2 molecules at low temperatures, so the catalytic hydrogenation of CO2 reaction is generally carried out above 250 °C. The reverse water-gas shift of CO2 is an endothermic reaction and is more likely to occur at high temperatures, resulting in an increase in CO production, which promotes the catalysis of the hydrogenation reaction, leading to a decrease in the methanol selectivity of the 2Cu-La2O2CO3 and Cu-Fe / La2O2CO3 catalysts. The methanol selectivity of the 2Fe / La2O2CO3 catalyst remains stable, possibly because the Fe component can inhibit the formation of CO at the corresponding temperature.

[0038] Such as Figure 5 It is a diagram of the properties of methanol production by hydrogenation of CO2 over the Cu-Fe / La2O2CO3 catalyst. As can be seen from the figure, the yield of the Cu-Fe / La2O2CO3 catalyst is better than that of the 2Cu-La2O2CO3 and 2Fe / La2O2CO3 catalysts, proving that the Cu-Fe / La2O2CO3 catalyst prepared in this invention has excellent catalytic performance in the reaction of hydrogenation of CO2 to methanol, realizing the resource utilization of CO2, and is of great significance for reducing carbon pressure emissions and promoting sustainable energy development.

[0039] The Cu-Fe / La2O2CO3 catalyst provided by this invention utilizes the synergistic effect of Cu-Fe bimetals to form a CuFe alloy, enhancing the adsorption capacity for methoxy intermediates (key intermediates in methanol production), thereby improving the selectivity of methanol; overcoming the problem that traditional Cu-based catalysts are prone to form by-products (such as CO, secondary hydrocarbons) in the reaction of hydrogenation of CO2 to methanol; the preparation process of this invention is simple and fast, and can be applied in large quantities industrially.

Claims

1. A method for preparing a Cu-Fe based catalyst, characterized in that: The method comprises the following preparation steps: NaOH solution is added dropwise to La(NO3)3·6H2O solution, and the obtained suspension is reacted in a hydrothermal reactor to obtain a La(OH)3 precursor, and the La(OH)3 precursor is washed, dried, and annealed to obtain a hexagonal La2O2CO3 carrier; the hexagonal La2O2CO3 carrier is soaked with water, and ferric nitrate solution and copper nitrate solution are added dropwise thereto, and the solvent is evaporated and then annealed to obtain a Cu-Fe / La2O2CO3 catalyst.

2. The method for preparing a Cu-Fe based catalyst according to claim 1, characterized in that: The molar ratio of La(NO3)3·6H2O and NaOH is 1:3.57-71.4; the molar ratio of the hexagonal La2O2CO3 carrier, ferric nitrate and copper nitrate is 1:0.0127:0.0146.

3. The method for preparing a Cu-Fe based catalyst according to claim 1, characterized in that: The reaction temperature is 160° C., and the reaction time is 12 h. The washing is performed until the pH of the La(OH) 3 precursor is 7.

4. The method for preparing a Cu-Fe based catalyst according to claim 1, characterized in that: The drying temperature is 80°C.

5. The method for preparing a Cu-Fe based catalyst according to claim 1, characterized in that: The first annealing was performed in air at a temperature of 550° C. and for 2 h.

6. The method for preparing a Cu-Fe based catalyst according to claim 1, characterized in that: The temperature of the solvent evaporation is 80°C.

7. The method for preparing a Cu-Fe based catalyst according to claim 1, characterized in that: The atmosphere of the second annealing is hydrogen, the annealing temperature is 500° C., and the annealing time is 2 h.

8. The method for preparing a Cu-Fe based catalyst according to claim 1, characterized in that: The heating rates of the two annealing processes were both 10°C / min.

9. A Cu-Fe based catalyst, characterized in that Prepared by the method according to any one of claims 1 to 8.

10. Use of the Cu-Fe based catalyst as claimed in claim 9, characterized in that: Applied in the CO2 hydrogenation to methanol reaction.

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