Fe-doped Co-CeO2 catalysts that synergistically regulate oxygen vacancies and weakly basic sites and their applications

Abstract

This invention discloses a Fe-doped Co-CeO2 catalyst that synergistically regulates oxygen vacancies and weakly basic sites, which is prepared by the following method: (1) a metal salt solution is added dropwise to an alkaline solution to obtain a suspension; the metal salt solution is composed of cerium salt, cobalt salt, iron salt and water, and the molar ratio of iron to cobalt is (0.25~0.75):1; (2) the suspension is subjected to hydrothermal treatment to obtain a precursor; (3) the precursor is calcined under a nitrogen atmosphere and then reduced to obtain the catalyst. The application of the catalyst in the hydrogenation of carbon dioxide to methanol. The catalyst of this invention achieves the synergistic design of "oxygen vacancy-weakly basic site-metal electronic structure" by constructing synergistic metal sites of Co and Fe on a CeO2 support and inducing the formation of controllable concentrations of oxygen vacancies and weakly basic sites. Under medium-low temperature and high pressure conditions, it can achieve high selectivity for methanol and has long-period and wide space velocity fluctuation stability.

Description

Technical Field

[0001] This invention relates to a catalyst in which Fe-doped Co-CeO2 synergistically regulates oxygen vacancies and weakly basic sites and its application in the hydrogenation of carbon dioxide to methanol, belonging to the field of catalyst technology. Background Technology

[0002] Carbon dioxide hydrogenation to methanol (CHDM) refers to the chemical reaction that synthesizes methanol from carbon dioxide and hydrogen under the action of a catalyst. It is one of the important technological pathways for achieving the goal of carbon resource recycling. Currently, CHDM technology faces the following technical bottlenecks: Firstly, the reaction system is thermodynamically limited, and water generation and side reactions inhibit the formation of the target product. Secondly, the high stability and difficulty in activation of carbon dioxide molecules, along with the complex hydrogenation conversion pathway, limit the kinetics of the catalytic process. More importantly, the reverse water-gas shift reaction (RWGS) in this reaction network usually competes with methanol synthesis in parallel, easily generating more CO byproducts, reducing carbon atom utilization efficiency and methanol selectivity.

[0003] In recent years, defect engineering studies on metal oxide catalysts have shown that oxygen vacancies can serve as important active structural units, altering the local electronic structure of the catalyst, enhancing CO2 adsorption and polarization, promoting H2 activation and surface hydrogen migration, and regulating reaction pathway selection by influencing the adsorption configuration of key intermediates. Based on this mechanism, constructing oxygen-rich vacancy interfaces has become an important approach to improve CO2 hydrogenation performance. However, relying solely on oxygen vacancies is insufficient to stably achieve a balance between high activity and high selectivity. Excessive oxygen vacancies may lead to over-adsorption of reactants or intermediates, hindering subsequent directional conversion; insufficient oxygen vacancies, on the other hand, result in inadequate activation and low conversion rates. Studies have shown that the acid-base properties of the catalyst surface, especially the density and distribution of weakly basic sites, have a decisive impact on CO2 adsorption modes, intermediate stability, and RWGS suppression capabilities. Therefore, how to achieve the synergistic design of "oxygen vacancies, weakly basic sites, and metal electronic structure" is a key technical problem that urgently needs to be solved. Summary of the Invention

[0004] In view of the above-mentioned prior art, the present invention provides a catalyst in which Fe-doped Co-CeO2 synergistically regulates oxygen vacancies and weakly basic sites, and its application in the hydrogenation of carbon dioxide to methanol.

[0005] This invention is achieved through the following technical solution: A Fe-doped Co-CeO2 catalyst that synergistically regulates oxygen vacancies and weakly basic sites is prepared by the following method: (1) Add the metal salt solution dropwise to the alkaline solution while stirring to obtain a suspension. The metal components are fully co-precipitated in the high alkalinity environment and form a homogeneous suspension system, which provides a precursor basis for the subsequent construction of a highly dispersed active interface. The metal salt solution is composed of cerium salt, cobalt salt, iron salt and water, wherein the total molar concentration of the metal salt is 0.3 to 0.5 mol / L, cobalt accounts for 2.0% to 3.0% of the total metal molar amount, and the molar ratio of iron to cobalt is (0.25 to 0.75):1; OH in the alkaline solution - The concentration is 4–5 mol / L; (2) Place the suspension in a reaction vessel and hydrothermally treat it at 130-150°C for 16-24 hours to promote precursor crystallization and metal-support interface reconstruction. After the reaction is completed, cool it naturally to room temperature, wash the product with water until the filtrate is neutral, and dry it to obtain the precursor. (3) The precursor is ground into powder and calcined under a nitrogen atmosphere: calcination temperature 865-880 K, time 4-6 hours, to achieve precursor decomposition, crystal phase stabilization and interface structure fixation; after calcination, the product is placed in a H2-N2 mixed gas for reduction treatment: temperature 565-580 K, time 1.5-2.5 hours, to obtain electron-rich metal active centers, that is, Fe-doped Co-CeO2 synergistic regulation of oxygen vacancies and weak basic sites catalyst.

[0006] Preferably, in step (1), the total molar concentration of the metal salt is 0.4 mol / L, cobalt accounts for 2.5% of the total metal molar amount, and the molar ratio of iron to cobalt is 0.25:1, 0.5:1, or 0.75:1.

[0007] Preferably, in step (1), the cerium salt is selected from Ce(NO3)3·6H2O, the cobalt salt is selected from Co(NO3)2·6H2O, and the iron salt is selected from Fe(NO3)3·9H2O.

[0008] Preferably, in step (1), the alkaline solution is selected from a sodium hydroxide solution with a concentration of 4.57 mol / L.

[0009] Preferably, in step (2), the hydrothermal treatment temperature is 140°C and the time is 20 hours.

[0010] Preferably, in step (3), the calcination temperature is 873 K and the time is 5 hours; the reduction treatment temperature is 573 K and the time is 2 hours.

[0011] Preferably, in step (3), the H2-N2 mixture accounts for 5% by volume.

[0012] The Fe-doped Co-CeO2 catalyst prepared by the above method can simultaneously improve the oxygen vacancy concentration and the effectiveness of the weak basic sites by regulating the electronic structure of Co and the surface defect structure of CeO2 through Fe doping. It can be used as a catalyst for the hydrogenation of carbon dioxide to methanol.

[0013] The Fe-doped Co-CeO2 synergistic regulation catalyst of this invention, which regulates oxygen vacancies and weakly basic sites, is prepared via a "co-precipitation-hydrothermal crystallization-calcination-reduction" route. Through the synergistic regulation of "electron-rich Co sites + interfacial oxygen vacancies + weakly basic sites," it achieves a directional enhancement of the carbon dioxide to methanol pathway. Its activity originates from the synergistic effect of Co-Fe synergistic active centers and oxygen vacancies, promoting CO2 adsorption polarization, H2 low-barrier activation, and continuous hydrogenation via the formate pathway. Compared to the undoped sample, the Fe-doped sample exhibits a lower reaction barrier in H2 heterolytic activation and the key intermediate hydrogenation step. The core role of Fe doping is to promote Co reduction and form electron-rich Co centers, increase the oxygen vacancy concentration at the CeO2 interface, and optimize the distribution of weakly basic CO2 adsorption sites. These three factors synergistically promote the formate pathway and suppress unfavorable side pathways.

[0014] The Fe-doped Co-CeO2 synergistic regulation catalyst of the present invention, used for the hydrogenation of carbon oxidizer to methanol, was tested. The experimental procedure was as follows: the catalyst was loaded into a high-pressure continuous flow stainless steel fixed-bed reactor at a loading of approximately 0.05 g, a reaction pressure of 3 MPa, and a feed gas composition of H2:CO2:N2 = 72:24:4 (N2 was used as an internal standard). The temperature was 220–260 °C. The reaction system was continuously run at the target temperature for 2 h to reach steady state before data collection, and the product composition was analyzed by online gas chromatography (TCD+FID). The experimental results showed that: 1) under conditions of 230 °C, 3 MPa, and H2 / CO2 = 3, approximately 9.5% CO2 conversion and greater than 90% methanol selectivity could be achieved, with a styrochemical synergy (STY) of 1084.6 g MeOH·kgcat. -1 ·h -1 2) At 240℃, the CO2 conversion rate can reach approximately 12%, and the STY is approximately 1400 gMeOH·kgcat. -1 ·h -1 Under extended operating conditions, STY can reach a maximum of 2162.3 gMeOH·kgcat. -1 ·h -1 3) Continuous operation for 240 hours and 36,000–144,000 hours -1 Under fluctuating space velocity conditions, the catalyst maintained high stability and showed no significant deactivation. 4) The apparent activation energy for the methanol pathway was significantly reduced (Co1Fe 0.5 / CeO2 is 60.61 kJ / mol, significantly lower than Co-CeO2's 88.63 kJ / mol), demonstrating higher intrinsic activity. 5) Clear structure-performance correlation: STY is strongly positively correlated with oxygen vacancy concentration (R 2 =0.98), and the weak / moderate CO2 adsorption sites were also highly correlated with the methanol yield, proving that the synergistic design of the present invention has a repeatable structure-activity relationship.

[0015] The Fe-doped Co-CeO2 synergistic regulation catalyst of the present invention achieves a synergistic design of "oxygen vacancy-weak basic site-metal electronic structure" by constructing synergistic metal sites of Co and Fe on CeO2 support and inducing the formation of controllable concentrations of oxygen vacancy and weak basic sites. Under medium-low temperature and high pressure conditions, it can achieve high selectivity for methanol and has long-period and wide space velocity fluctuation stability. It has the characteristics of moderate oxygen vacancy, weak adsorption, electron-rich metal center, and low methanol pathway energy barrier. It solves the following technical problems existing in the current carbon dioxide hydrogenation to methanol technology: 1) CO2 molecules are inert and difficult to activate; 2) The reverse water-gas shift reaction and methanol synthesis compete in parallel, resulting in increased CO by-products and decreased methanol selectivity; 3) When relying solely on oxygen vacancy or single acid-base regulation, the dilemma of "insufficient activation / excessive adsorption" is easy to occur; 4) Insufficient stability under industrial-use conditions (temperature and space velocity fluctuations).

[0016] Simultaneously, this invention characterizes the number of oxygen vacancies, weak / moderate CO2 adsorption capacity, number of d-holes in active metal centers, and apparent activation energy of methanol formation in the catalyst, and then evaluates the catalyst based on the synergistic relationship of multiple indicators. Specifically, the number of oxygen vacancies is quantified using electron paramagnetic resonance (EPR); the weak / moderate CO2 adsorption capacity is obtained by integrating the desorption peak area in the 40–400 °C range during CO2 temperature-programmed desorption; the number of d-holes is obtained by integrating the XANES white line and calibrating with standard samples; and the apparent activation energy of methanol formation is obtained by fitting the Arrhenius curve of the methanol formation rate at different temperatures. In the final screening, the maximum number of oxygen vacancies or the maximum total adsorption capacity is not used as the sole criterion; instead, catalytic systems with high oxygen vacancies, high adsorption capacity in the 40–400 °C range, low number of d-holes, and low apparent activation energy of methanol are preferentially selected. Experimental results show that the number of oxygen vacancies is significantly positively correlated with STY (Self-Adsorption Rate), the adsorption amount at 40–400℃ is highly correlated with methanol yield, while the contribution of strong adsorption sites is weak. Simultaneously, fewer d-vacancies and lower apparent activation energy for methanol formation are more conducive to methanol formation. This invention unifies oxygen vacancies, adsorption sites, electronic structure, and kinetic parameters into a single evaluation or screening process, clearly indicating that the truly effective indicator is not the total CO2 adsorption amount, but rather the number of weak / moderate CO2 adsorption sites within the 40–400℃ range.

[0017] The various terms and phrases used in this invention have their general meanings known to those skilled in the art. Attached Figure Description

[0018] Figure 1 XRD patterns of each catalyst.

[0019] Figure 2 Co1Fe 0.5 HRTEM, HAADF-STEM and EDS mapping images of the / CeO2 catalyst, where (a), (b) and (c) are HRTEM images, and (d) is a HAADF-STEM and EDS mapping image.

[0020] Figure 3 Co1Fe 0.5 SAED image, AC-HAADF-STEM image and defect schematic diagram, lattice deformation and interfacial strain of / CeO2 catalyst, wherein (a) is SAED image, and (b) to (g) are AC-HAADF-STEM image and defect schematic diagram, lattice deformation and interfacial strain.

[0021] Figure 4 TEM image of reference standard 1.

[0022] Figure 5 H2-TPR curves, CO-DRIFTS spectra, and Co2pXPS spectra of each catalyst are shown in Figure 1. (a) is the H2-TPR curve, (b) is the CO-DRIFTS spectra, and (c) is the Co2pXPS spectra.

[0023] Figure 6 Co / CeO2 and Co1Fe 0.5 XAFS characterization of the local structure and electronic states of Co species in / CeO2 catalyst, where (a) is the Co K-edge XANES spectrum, (b) is the EXAFS spectrum, (c) is the wavelet transform analysis, (d) is the Co oxidation state obtained by linear fitting of the white line integral, and (e) is the d-hole count.

[0024] Figure 7 Characterization of the correlation between oxygen vacancy regulation and electronic structure evolution on catalyst performance, where (a) is the EPR spectrum of each catalyst; (b) and (c) are reference standard 1 and Co1Fe. 0.5 Charge density difference plot of / CeO2; (d) shows the relationship between DOS and d-band center; (e) shows the correlation between oxygen vacancy content and d-band center.

[0025] Figure 8 Raman spectra of each catalyst.

[0026] Figure 9: Schematic diagram of the catalytic performance of each catalyst, where (a) is CO2 conversion, (b) is methanol selectivity, (c) is methanol space-time yield (STY), (d) is the performance as a function of WHSV, H2 / CO2 and pressure, and (e) is a comparison with advanced catalysts in the literature.

[0027] Figure 10 Stability under fluctuating operating conditions over 240 hours.

[0028] Figure 11 Comparison of supplemental performance of different samples under 230℃ and wide space velocity conditions, where (a) is CO2 conversion rate at 230℃, (b) is product selectivity at 230℃, (c) is CO2 conversion rate under wide space velocity conditions, and (d) is product selectivity under wide space velocity conditions.

[0029] Figure 12 Co1Fe after the reaction 0.5 TEM image of / CeO2.

[0030] Figure 13 : Schematic diagram of catalyst structure-performance relationship, where (a) is the correlation between STY and oxygen vacancies, (b) is the linear fitting result of d-band center and space-time yield, (c) is the CO2-TPD curve, (d) is the correlation between STY and CO2 adsorption amount at 40-400℃, (e) is the correlation between STY and CO2 adsorption amount at 40-750℃, and (f) is the correlation between oxygen vacancy amount and carbon dioxide adsorption amount at 40-400℃.

[0031] Figure 14 Structure-activity relationship analysis of Co 3d orbital hole characteristics and reaction pathway kinetics, where (a) is the correlation between the number of Co 3d orbital holes and methanol yield at reaction temperatures of 200–240 °C, and (b) and (c) are the apparent activation energies of the methanol and CO pathways.

[0032] Figure 15Supplementary correlation plots at different temperatures, where (a) shows the correlation between oxygen vacancy content and methanol space-time yield (STYMeOH) for different catalysts at 220℃; (b) shows the correlation between oxygen vacancy content and methanol space-time yield (STYMeOH) for different catalysts at 240℃; (c) shows the correlation between CO2 adsorption (weak and moderate adsorption) and methanol space-time yield (STYMeOH) for different catalysts at 220℃; (d) shows the correlation between CO2 adsorption (weak and moderate adsorption) and methanol space-time yield (STYMeOH) for different catalysts at 240℃; (e) shows the correlation between CO2 adsorption and methanol space-time yield (STYMeOH) for different catalysts in the range of 40–750℃ from 220℃; and (f) shows the correlation between CO2 adsorption and methanol space-time yield (STYMeOH) for different catalysts in the range of 40–750℃ from 240℃.

[0033] Figure 16 : Schematic diagram of the correlation between d-holes and defects / adsorption capacity, where (a) is the correlation between the number of d-holes and the oxygen vacancy content (EPR); (b) is the correlation between the number of d-holes and the oxygen vacancy concentration; and (c) is the correlation between the number of d-holes and the CO2 adsorption capacity (weak adsorption and moderate adsorption).

[0034] Figure 17 High-pressure in-situ FT-IR, where (a) and (b) represent the CO2 adsorption and subsequent H2 hydrogenation process, under the conditions of 3 MPa, 230 °C, and 30 mL·min. -1 H2:CO2 = 3:1. (c) Co / CeO2 and Co1Fe 0.5 The free energy diagram of CO2 hydrogenation to methanol via the formate pathway in the / CeO2 model.

[0035] Figure 18 In-situ FTIR on Co-CeO2 and in-situ FTIR during the pressurization process, where (a) is the in-situ FTIR on Co-CeO2 and (b) is the in-situ FTIR during the pressurization process.

[0036] Figure 19 : Schematic diagram of the model formation energy, where (a) is Co1Fe 0.5 / CeO2, (b) is Co-CeO2.

[0037] Figure 20 Schematic diagram of CO2 adsorption energy, where (a) represents Co1Fe 0.5 / CeO2, (b) is Co / CeO2.

[0038] Figure 21 Schematic diagram of H2 dissociation energy barrier.

[0039] Figure 22 Schematic diagram of alternative hydrogenation routes. Detailed Implementation

[0040] The present invention will be further described below with reference to embodiments. However, the scope of the present invention is not limited to the following embodiments. Those skilled in the art will understand that various changes and modifications can be made to the present invention without departing from the spirit and scope thereof.

[0041] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0042] Example 1: Preparation of a Fe-doped Co-CeO2 catalyst for synergistic regulation of oxygen vacancies and weakly basic sites. The steps are as follows: (1) Dissolve 12.8g of sodium hydroxide in 70mL of deionized water to obtain a sodium hydroxide solution; Ce(NO3)3·6H2O, Co(NO3)2·6H2O and Fe(NO3)3·9H2O were dissolved in 10 mL of deionized water to obtain a metal salt solution, wherein the total molar amount of the metal salt was 0.004 mol, cobalt accounted for 2.5% of the total metal molar amount (i.e. 0.01 mmol), and the molar ratio of iron to cobalt was 0.25:1. The above metal salt solution was added dropwise to a sodium hydroxide solution while stirring vigorously to obtain a suspension. The metal components were fully co-precipitated in the high alkalinity environment and formed a homogeneous suspension system, providing a precursor basis for the subsequent construction of a highly dispersed active interface.

[0043] (2) The above suspension was placed in a polytetrafluoroethylene-lined reactor (capacity 100 mL) and hydrothermally treated at 140°C for 20 hours to promote precursor crystallization and metal-support interface reconstruction. After the reaction was completed, the product was naturally cooled to room temperature, and the product was repeatedly washed with water until the filtrate was neutral. It was then dried at 100°C overnight to obtain the precursor.

[0044] (3) The precursor was ground into powder and calcined under a nitrogen atmosphere: heating rate 5 K / min, calcination temperature 873 K, holding time 5 h, nitrogen flow rate 30 mL / min, to achieve precursor decomposition, crystal phase stabilization and interface structure fixation; after calcination, the product was placed in a 5% H2-N2 mixed gas (composed of H2 and N2, H2 accounting for 5% by volume) for reduction treatment: temperature 573 K, time 2 h, to obtain Co1Fe 0.25 / CeO2 catalyst.

[0045] By adjusting the molar ratio of iron to cobalt in the metal salt solution to 0.5:1 and 0.75:1, Co1Fe was prepared using the same method. 0.5 / CeO2 catalyst, Co1Fe 0.75 / CeO2 catalyst.

[0046] The molar amount of iron in the metal salt solution was adjusted to 0, and control standard 1 (Co-CeO2) was prepared using the same method. The molar amounts of both iron and cobalt in the metal salt solution were adjusted to 0, and control standard 2 (CeO2) was prepared using the same method. These were used for subsequent performance and structure-activity relationship verification.

[0047] Experiment 1: Performance Characterization of Catalysts (1) X-ray diffraction analysis was performed on the three catalysts prepared in Example 1, as well as reference standard 1 and reference standard 2. The XRD patterns of each catalyst are shown below. Figure 1 As shown, all samples exhibited characteristic diffraction peaks of the CeO2 support, while no obvious independent crystalline phase diffraction peaks of Co and Fe were observed, indicating that Co and Fe species mainly exist in a highly dispersed state on the surface or interface of the CeO2 support. This demonstrates that the catalyst obtained in Example 1 possesses the structural basis for forming a highly dispersed active interface.

[0048] (2) High-resolution transmission electron microscopy (TEM) was used to observe the three catalysts and reference standards 1 and 2. Co1Fe 0.5 HRTEM, HAADF-STEM, and EDS mapping images of the / CeO2 catalyst are as follows: Figure 2 As shown. Co1Fe 0.5 SAED images, AC-HAADF-STEM images and defect diagrams, lattice deformation and interfacial strain of the / CeO2 catalyst are shown, where (a) is the SAED image, and (b) to (g) are the AC-HAADF-STEM images and defect diagrams, lattice deformation and interfacial strain as shown. Figure 3 As shown. TEM image of reference 1 is shown below. Figure 4 As shown. By Figure 2 It can be seen that Co1Fe 0.5 In the CeO2 catalyst, Co nanoparticles are uniformly distributed on the surface of CeO2 nanorods, with particle sizes mainly ranging from 5 to 20 nm; elemental mapping further indicates that Co, Fe, and Ce are spatially uniformly distributed. Figure 3 As shown in (a), HAADF-STEM and EDSmapping results indicate that Co, Fe, and Ce elements are uniformly distributed on the support surface. Figure 3 As shown in (b), the SAED results indicate that the sample has good crystallization characteristics; Figure 3(a) and the high-resolution image show that the local interplanar spacing is about 0.203 nm and 0.31 nm, respectively, corresponding to the Co (111) and CeO2 (111) crystal planes, proving that Co has been successfully anchored on the carrier surface. Figure 3 (b) to (g) show the presence of lattice distortion and strain concentration regions at the interface, indicating that Fe doping induces the formation of many structural defects at the Co and CeO2 interface, and this structural feature is closely related to the generation of oxygen vacancies. Figure 4 The control sample 1 still exhibits a nanorod morphology, but its interface defect characteristics are weaker than those of the Fe-doped sample, indicating that the participation of Fe helps to construct a more active interface structure.

[0049] (3) A systematic analysis was conducted on the reducibility, surface adsorption behavior, electronic structure evolution, and local coordination environment of Co species in each catalyst to further elucidate the mechanism by which Fe doping regulates the structure of the active center and enhances methanol production performance. The H2-TPR curves, CO-DRIFTS spectra, and Co2pXPS spectra of each catalyst are shown below. Figure 5 As shown. XAFS characterization of the local structure and electronic states of Co species in each catalyst is as follows. Figure 6 As shown. By Figure 5 (a) It can be seen that after Fe doping, the reduction peak of Co species shifts to the low temperature direction, indicating that Co is more easily reduced and forms active metal centers; Figure 5 (b) at 1935 cm -1 and 1867 cm -1 The enhanced adsorption peak indicates that the active site has improved adsorption capacity for CO probe molecules. Figure 5 (c) The decrease in Co2p binding energy and the weakening of satellite peaks indicate the presence of electron transfer from Fe to Co. Figure 6 (a) to (c) further demonstrate Co1Fe 0.5 In CeO2, the localized Co structure is closer to the low valence state, and the coordination environment is more favorable for the reaction. Figure 6 The oxidation states and d-hole statistics given in (d) to (e) demonstrate the key structural feature of "Co electron enrichment": Co1Fe is obtained by integral fitting of the white line. 0.5 The average oxidation state of Co in / CeO2 is approximately +1.16, which is lower than that of Co / CeO2 (approximately +1.50), and its d-hole count is also lower, indicating that Fe doping effectively improves the electron enrichment of Co active centers.

[0050] (4) A systematic analysis was conducted on the oxygen vacancy formation behavior, defect structure evolution, and intrinsic correlation between these factors and electronic structure regulation of each catalyst to reveal the structural basis for the improvement of CO2 adsorption activation and methanol generation performance by Fe doping. The correlation characterization of oxygen vacancy regulation and electronic structure evolution with catalyst performance is as follows: Figure 7As shown. The Raman spectra of each catalyst are as follows. Figure 8 As shown. By Figure 8 It can be seen that the ratio of defect-induced D peak to F2g peak (ID / F2g) increases with increasing Fe content, reflecting an increase in the number of oxygen vacancies; Figure 7 (a) A significant EPR signal appears at g=2.003, and the intensity ratio of the defect-induced D peak to the F2g peak increases with increasing Fe content, further demonstrating that Fe doping promotes the formation of oxygen vacancies in the CeO2 support. Quantitative results show that the oxygen vacancy content increases from 5.25 × 10⁻⁶ in CeO2. 18 spin / g increased to 5.9 × 10⁻⁶ for Co-CeO₂. 18 spin / g, then increase to Co1Fe 0.25 / CeO2 6.72×10 18 spin / g, Co1Fe 0.5 / CeO2 8.18×10 18 spin / g and Co1Fe 0.75 / CeO2 9.68×10 18 spin / g. Figure 7 (b) and (c) show that the Fe-doped model exhibits more pronounced electron enrichment near oxygen vacancies. Figure 7 (d) and (e) show that the center of the d-band is coupled with the changes in oxygen vacancies, providing an electronic structure basis for the subsequent CO2 adsorption activation and reaction kinetics improvement.

[0051] Experiment 2: Production of methanol from carbon dioxide via hydrogenation using a catalyst The catalyst prepared in Example 1 was used in a high-pressure continuous flow fixed-bed reactor for the hydrogenation of carbon dioxide to methanol. Specifically, 0.05 g of catalyst was loaded into the isothermal zone of the reaction tube, and feed gas was introduced after system pressurization for continuous reaction. The feed gas integral ratio was H2:CO2:N2 = 72:24:4 (volume ratio), with N2 used as an internal standard for online quantitative analysis and carbon balance calculation. The reaction pressure was controlled at 3 MPa, and the temperature could be adjusted within the range of 220–260 °C. Under typical evaluation conditions, 230 °C was used for comprehensive performance comparison, and 240 °C was used for high-load capacity assessment. After feeding, the reactor was kept in steady-state operation for at least 2 hours before online sampling and analysis to avoid interference from the start-up state.

[0052] Product analysis employed an online gas chromatography system (TCD and FID coupled) to continuously monitor the reaction tail gas, and CO2 conversion, methanol selectivity, and methanol space-time yield (STY) were calculated using a standardized method. At least three sets of data were continuously collected for each operating condition to ensure repeatability and statistical reliability. To verify engineering adaptability, further operation was conducted under a wide space velocity (WHSV) range of 36,000–144,000 h⁻¹.-1 The catalyst was subjected to dynamic switching tests of temperature and space velocity. After running continuously for 240 hours under such fluctuating conditions, the catalyst's resistance to disturbances and long-term stability can be evaluated.

[0053] Results: Schematic diagrams of the catalytic performance of each catalyst are shown below. Figure 9 As shown. The stability under fluctuating operating conditions over 240 hours is as follows. Figure 10 As shown. Comparison of supplementation performance of different samples under 230℃ and wide space velocity conditions. Figure 11 As shown. After the reaction, Co1Fe 0.5 TEM image of / CeO2 as follows Figure 12 As shown. By Figure 9 (a) to (c) and Figure 11 It can be seen that Co1Fe 0.5 / CeO2 achieves an optimal balance between activity, selectivity, and STY, exhibiting a CO2 conversion rate of approximately 9.5%, a methanol selectivity exceeding 90%, and an STY of 1084.6 gMeOH·kgcat at 230℃ and 3 MPa. -1 ·h -1 When the temperature is increased to 240℃, the CO2 conversion rate is approximately 12%, and the STY is approximately 1400 gMeOH·kgcat. -1 ·h -1 This demonstrates the role of appropriate Fe doping in simultaneously improving performance. For example... Figure 9 As shown in (b), the methanol selectivity of this sample remained above 90% throughout the tested temperature range, significantly higher than most comparative samples; Figure 9 As shown in (c), its methanol space-time yield can reach approximately 1400 gMeOH·kgcat at 240°C. -1 ·h -1 .Depend on Figure 9 (d) It can be seen that under different space velocities, H2 / CO2 ratios, and pressure conditions, Co1Fe 0.5 Both / CeO2 and Co1Fe maintain good adaptability to operating conditions. 0.5 The STY of / CeO2 initially rises rapidly with increasing space velocity and then stabilizes. It continues to increase with increasing H2 / CO2 ratio and pressure, indicating that it remains usable within a relatively wide process window. Figure 9 (e) shows that the sample has high methanol selectivity and higher STY in a similar conversion range. Figure 10 This indicates that at 220–260℃ and 36,000–144,000 h... -1 No significant inactivation was observed after 240 hours of continuous operation under dynamic fluctuation conditions. Figure 12The reaction showed that the nanorod framework and good particle dispersion were maintained, and no significant sintering collapse was observed. These results indicate that the catalyst not only has excellent static properties but also good stability under dynamic conditions.

[0054] A schematic diagram of the catalyst structure-performance relationship is shown below. Figure 13 As shown. The structure-property relationship analysis of Co 3d orbital hole characteristics and reaction pathway kinetics is as follows. Figure 14 As shown in the figure. Supplementary correlation plots at different temperatures are shown below. Figure 15 As shown in the diagram. The correlation between d-holes and defect / adsorption capacity is illustrated in the figure below. Figure 16 As shown. By Figure 13 (a) It can be seen that STY is strongly positively correlated with the number of oxygen vacancies (R 2 =0.98), indicating that the formation of oxygen vacancies promotes CO2 activation and methanol production; such as Figure 13 As shown in (c), the CO2-TPD results indicate that the catalyst possesses both low-temperature / medium-temperature weak and moderate-intensity adsorption sites and high-temperature strong adsorption sites. Figure 13 (c) to (e) and Figure 14 (a) shows that there is a significant positive correlation between the number of oxygen vacancies and the amount of CO2 adsorbed at 40–400 °C. The amount of weak / moderate CO2 adsorption in the range of 40–400 °C is more correlated with the methanol yield, while the strong adsorption sites (total adsorption at 40–750 °C) contribute less to the methanol yield. This indicates that "activatable but not overly confined" adsorption sites are more conducive to the targeted production of methanol. Figure 14 (b) and Figure 16 This indicates that the fewer d-holes (the higher the Co electron density), the higher the methanol yield, and that electron-rich Co contributes to the stable formation of oxygen vacancies. Figure 14 (b) and (c) give the kinetic results: Co1Fe 0.5 The apparent activation energy for methanol formation from / CeO2 is 60.61 kJ / mol, which is significantly lower than that of Co-CeO2 (88.63 kJ / mol), indicating that this catalyst has lower kinetic resistance in the methanol pathway.

[0055] High-voltage in-situ FT-IR such as Figure 17 As shown. In-situ FTIR on Co-CeO2 and in-situ FTIR during the pressurization process are shown. Figure 18 As shown. By Figure 17 As shown in (a) and (b), after the introduction of CO2, monodentate carbonate (m-CO3*) and some bicarbonate signals appear first; after pressurization to 3 MPa, the weak / moderate basicity sites further promote the conversion of carbonate to hydrogenatable intermediates, and formate (HCOO*) related peaks gradually appear. After switching to H2, the m-CO3 peak weakens, while formate, methoxy (H3CO), and linear carbonyl (CO*) signals appear and evolve, combined with... Figure 18The formation and consumption process of intermediates indicates that the system primarily follows the formate pathway to methanol production, which is consistent with experimental results showing high methanol selectivity. Figure 17 As shown in (c), theoretical calculations indicate that Co1Fe 0.5 The / CeO2 model more readily stabilizes oxygen-containing vacancy structures and exhibits more favorable energy barriers for CO2 adsorption, H2 dissociation, and key hydrogenation steps, thereby reducing the energy barrier for the conversion of HCOO* to subsequent intermediates. The experimental and theoretical results corroborate each other, indicating a synergistic effect among oxygen vacancies, weakly basic sites, and electron-rich Co centers, collectively promoting the directed hydrogenation of CO2 to methanol.

[0056] Model formation energy diagram as shown Figure 19 As shown in the diagram. A schematic diagram of CO2 adsorption energy is shown below. Figure 20 As shown in the diagram. A schematic diagram of the H2 dissociation energy barrier is shown below. Figure 21 As shown. A schematic diagram of alternative hydrogenation routes is shown below. Figure 22 As shown. By Figure 19 It can be seen that both models can stably form oxygen vacancy structures, with formation energies of approximately -1.23 eV (Co1Fe). 0.5 / CeO2) and -1.19 eV (Co-CeO2). Figure 21 H2 heteroclasts were observed in Co1Fe. 0.5 The energy barrier on / CeO2 is only about 0.12 eV, which is significantly lower than that of Co-CeO2 (0.45 eV), indicating that the participation of Fe is more conducive to the generation of active hydrogen. Figure 17 (c) and Figure 22 This collectively indicates that the energy barrier for CO2 via the HCOO pathway is lower than that via the COOH pathway, and that in Co1Fe... 0.5 The energy barrier for the key step b-HCOO*→H2COO* in / CeO2 is significantly reduced (approximately 1.20 eV, compared to approximately 2.35 eV for Co-CeO2), making subsequent hydrogenation of intermediates easier to proceed. Figure 20 It can be seen that the system achieves energy matching of "adsorption, activation and desorption", thereby increasing the methanol pathway rate while suppressing RWGS competition.

[0057] Based on the above implementation process and the results of characterization-reaction coupling, the preferred catalyst of this invention is Co1Fe. 0.5 / CeO2, its core lies in simultaneously constructing electron-rich Co sites, interfacial oxygen vacancies, and weakly / moderately basic adsorption sites through Fe regulation. Under medium-low temperature and high pressure conditions, it can achieve both high methanol selectivity and high STY, while maintaining stable output under dynamic loads. This enables efficient and highly selective hydrogenation of CO2 to methanol under industrial-related medium-low temperature, high pressure, and fluctuating operating conditions. This implementation method has clear process operability, structural characterizability, and performance reproducibility, and can be directly used for subsequent pilot-scale amplification, suitable for continuous operation scenarios aimed at industrial scale-up.

[0058] The above embodiments are provided to those skilled in the art to fully disclose and describe how the claimed implementations can be carried out and used, and are not intended to limit the scope of the disclosure herein. Modifications that will be obvious to those skilled in the art will be within the scope of the appended claims.

Claims

1. A method for preparing a catalyst in which Fe-doped Co-CeO2 synergistically regulates oxygen vacancies and weakly basic sites, characterized in that, Includes the following steps: (1) Add the metal salt solution dropwise into the alkaline solution while stirring to obtain a suspension; The metal salt solution is composed of cerium salt, cobalt salt, iron salt and water, wherein the total molar concentration of the metal salt is 0.3 to 0.5 mol / L, cobalt accounts for 2.0% to 3.0% of the total metal molar amount, and the molar ratio of iron to cobalt is (0.25 to 0.75):1; OH in the alkaline solution - The concentration is 4–5 mol / L; (2) Place the suspension in a reaction vessel and hydrothermally treat it at 130-150°C for 16-24 hours; after the reaction is completed, allow it to cool naturally to room temperature, wash and dry it to obtain the precursor. (3) Grind the precursor into powder and calcine it under a nitrogen atmosphere: calcine temperature 865-880 K, time 4-6 hours; after calcine, place the product in a H2-N2 mixed gas for reduction treatment: temperature 565-580 K, time 1.5-2.5 hours, and the Fe-doped Co-CeO2 synergistic regulation of oxygen vacancies and weak basic sites is obtained.

2. The preparation method of the Fe-doped Co-CeO2 synergistic regulation catalyst for oxygen vacancies and weakly basic sites according to claim 1, characterized in that: In step (1), the total molar concentration of the metal salt is 0.4 mol / L, cobalt accounts for 2.5% of the total metal molar amount, and the molar ratio of iron to cobalt is 0.25:1, 0.5:1, or 0.75:

1.

3. The method for preparing the Fe-doped Co-CeO2 synergistic regulation catalyst for oxygen vacancies and weakly basic sites according to claim 1, characterized in that: In step (1), the cerium salt is selected from Ce(NO3)3·6H2O, the cobalt salt is selected from Co(NO3)2·6H2O, and the iron salt is selected from Fe(NO3)3·9H2O.

4. The preparation method of the Fe-doped Co-CeO2 synergistic regulation catalyst for oxygen vacancies and weakly basic sites according to claim 1, characterized in that: In step (1), the alkaline solution is selected from a sodium hydroxide solution with a concentration of 4.57 mol / L.

5. The method for preparing the Fe-doped Co-CeO2 synergistic regulation catalyst of oxygen vacancies and weakly basic sites according to claim 1, characterized in that: In step (2), the hydrothermal treatment temperature is 140℃ and the time is 20 hours.

6. The method for preparing the Fe-doped Co-CeO2 synergistic regulation catalyst of oxygen vacancies and weakly basic sites according to claim 1, characterized in that: In step (3), the calcination temperature is 873 K and the time is 5 hours; the reduction treatment temperature is 573 K and the time is 2 hours.

7. The method for preparing the Fe-doped Co-CeO2 synergistic regulation catalyst of oxygen vacancies and weakly basic sites according to claim 1, characterized in that: In step (3), the H2-N2 mixture accounts for 5% by volume.

8. A Fe-doped Co-CeO2 catalyst that synergistically regulates oxygen vacancies and weakly basic sites, prepared by any one of the preparation methods of claims 1 to 7.

9. The application of the Fe-doped Co-CeO2 synergistic regulation catalyst of claim 8 in the hydrogenation of carbon dioxide to methanol.

10. The application according to claim 9, characterized in that: In practical applications, a catalyst is loaded into a high-pressure continuous flow stainless steel fixed-bed reactor for reaction. The catalyst loading amount is 0.05 g, the reaction pressure is 3 MPa, the feed gas composition is H2:CO2:N2=72:24:4, and the temperature is 220~260℃.

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