Preparation method and application of oxygen-carrying-catalytic dual-function particles

Abstract

This invention relates to the preparation and application of oxygen-carrying catalytic bifunctional particles in chemical looping combustion technology, specifically the use of perovskite oxygen carriers for the hydrogenation of CO2 to produce ethylene, propylene, and butene. The catalyst has suitable CO2 adsorption and dissociation capabilities, inhibiting olefin re-adsorption, reducing secondary olefin reactions, and improving olefin selectivity. The catalyst effectively inhibits the secondary hydrogenation of primary olefins, regulating the production of high-value-added C2-C4 lower carbon olefins.

Description

Technical Field

[0001] The present invention relates to the preparation and application of oxygen-carrying and catalytic dual-function particles in chemical looping combustion technology, and to the preparation of ethylene, propylene and butene by using CO2 hydrogenation of perovskite oxygen carriers. Background Art

[0002] Fe-based oxygen carriers with ABO3 perovskite structures have attracted much attention due to their tunable structure. By doping the A and B sites of the bulk phase, the lattice defects and oxygen vacancies in the oxygen carrier are changed to achieve lattice oxygen activity and improve chemical looping combustion efficiency. Among various perovskite materials, LaFeO3 is considered to be an attractive candidate for oxygen carriers, mainly due to its high oxygen mobility and ability to accommodate a large number of vacancies in the structure at higher reaction temperatures. Due to different operating temperature conditions, the removal of oxygen and the total amount of available oxygen during CH4 oxidation will cause LaFeO3 to change from Fe to Fe. 3+ Reduction to Fe 2+ , but further reduction seems to be inhibited. Kinetic studies on the reduction of LaFeO3 by CH4 revealed that surface oxygen is related to oxygen vacancies. Initially, the removal of oxygen produces vacancies on the surface of the oxygen carrier, which will help promote the occurrence of the reaction. Subsequently, as the vacancy concentration increases, the activity of oxygen becomes a rate-determining step. The oxygen in LaFeO3 has two unequal atomic positions. The first oxygen (O1) is based on the coordination of two La ions and two Fe ions and is located in the La ion layer. The second oxygen (O2) is based on the coordination of three La ions and two Fe ions and is located between the Fe ion layers. As an excellent oxygen carrier, Fe-based perovskite still has difficulties in adapting its catalytic activity by utilizing its own material characteristics.

[0003] Due to the stability of perovskite oxide, it is difficult to expose more active metals. In addition, the low pore volume and low specific surface area caused by the high calcination temperature are disadvantageous factors for perovskite oxide, which inhibit the ability to capture reactants, resulting in low catalytic efficiency. The research team tried the B-site doping strategy and found that it can effectively improve the CO2 hydrogenation activity, but the reverse water gas shift activity is high, generating a large amount of CO. At the same time, limited by the Fischer-Tropsch ASF distribution law, C5 + The product distribution is broad, and the amount of converted C2-C4 products is low. To reduce CO generation and achieve synergy between the reverse water gas shift reaction and the Fischer-Tropsch synthesis reaction in the CO2 hydrogenation to olefins process, it is still necessary to further develop new oxygen-carrying catalytic particles to break the unique stability of perovskites and improve catalytic activity.

[0004] Perovskite-type oxides with flexible doping capabilities can be easily doped with highly active elements. At the same time, another outstanding ability of Fe-based perovskites is the dissolution of nanometal particles. Through high-temperature reduction treatment or in a reaction environment with a reducing atmosphere, perovskites usually undergo partial metal reduction. Therefore, there is a phenomenon in which reduced lattice cations migrate to the surface of the catalyst material. This metal segregation is considered to be the "anchoring" of active metal particles, which can maximize the catalytic activity of single atoms or metal oxide nanoparticles, which is extremely beneficial for activating stable CO2 molecules. Metals that are easy to dissolve out and metals that can reduce the reduction energy barrier are selected and doped into Fe-based perovskites. At the same time, they are embedded in inert carbon materials in an in-situ growth manner. In theory, compared with traditional co-precipitation, sol-gel methods and other technologies, small-sized and highly dispersed catalyst nanoparticles can be formed.

[0005] How to utilize the unique structural characteristics of perovskite, innovate preparation methods and improve oxygen carriers is a path worth exploring. Summary of the Invention

[0006] The present invention addresses the shortcomings of the prior art and is guided by reducing CO generation and achieving the synergistic effect of the reverse water-gas shift-Fischer-Tropsch synthesis reaction in the CO2 hydrogenation to olefins process. An improved hydrothermal synthesis method is used to prepare oxygen-carrying-catalytic bifunctional particles, regulate the catalytic activity of LaFeO3 perovskite, reduce CO generation, and improve the yield of light olefins.

[0007] Using inexpensive glucose as a carbon source, this study prepared LaGdFeCuO3 composite particles modified with Gd at the A-site and partially substituted with Cu at the B-site via a hydrothermal method. The performance of the carbon-coated LaGdFeCuO3@C series of oxygen carriers in CO2 hydrogenation to light olefins was investigated. Results showed that Gd modification modulated the particle phase, promoting active metal exudation and lattice oxygen migration. The LaGdFeCuO3 prepared by the hydrothermal method exhibited a cage-like branched structure, which exhibited weak carbon chain growth due to steric hindrance. The product distribution was dominated by C2-C4 hydrocarbons, resulting in superior catalytic CO2 hydrogenation performance compared to the sol-gel method. After Cu doping, the catalytic activity initially increased and then decreased with increasing Fe / C molar ratios; at an Fe / Cu ratio of 0.75, good olefin selectivity was observed. The post-reaction samples contained Fe2O3 and Fe3O4 phases, further confirming that the hydrothermally prepared perovskite catalyst enhanced the metal / perovskite interface effect, reduced structural stability, and effectively improved CO2 hydrogenation activity.

[0008] The above research provides a certain theoretical basis for the design and development of Fe-based oxygen-carrying-catalytic bifunctional particles coupled with chemical looping combustion CO2 capture and catalytic hydrogenation.

[0009] The catalyst of the present invention has suitable CO2 adsorption and dissociation ability, inhibits the re-adsorption of olefins, reduces the secondary reaction of olefins, and improves olefin selectivity. In order to break through the ASF product distribution, obtain low-carbon olefins with high selectivity and inhibit the by-product methane, C5 + The catalyst of this invention effectively inhibits the secondary hydrogenation of primary olefins, regulating the production of high-value-added C2-C4 low-carbon olefins. The active Fe host lattice of Fe-based perovskites effectively promotes the dissolution of active Fe ions or the migration of iron oxides into the perovskite matrix. By doping with Cu, the reduction energy barrier is lowered, and the metal oxides synergistically activate CO2, helping to enhance the perovskite's ability to catalyze the production of low-carbon olefins.

[0010] In order to achieve the above-mentioned purpose of the present invention, the technical solution adopted by the present invention is as follows:

[0011] (1) Weigh La:Gd:Fe=1-3:1:1, Fe:Cu=0.1-2, glucose:(La+Gd+Fe+Cu)=3 in a stoichiometric ratio, dissolve in water, stir until uniform, and then place in a high-pressure reactor.

[0012] (2) Place the reactor in an oven at 180°C for 8-12 hours, then cool to room temperature.

[0013] (3) Separate the black precipitate from the reactor, wash it with deionized water, and dry it in an oven at 80°C.

[0014] (4) After drying, the sample was placed in a muffle furnace and heated to 400 °C at a rate of 5 °C / min and kept at this temperature for 1 h. Then, the sample was heated to 750 °C at a rate of 2 °C / min and kept at this temperature for 5 h. After cooling, the sample was ground to obtain the target particles.

[0015] The metal ion is preferably lanthanum nitrate, gadolinium nitrate, iron nitrate, or copper nitrate.

[0016] The separation in step (3) is preferably centrifugal separation. The applicant has investigated filtration separation and centrifugal separation. It was found that the particles prepared by centrifugal separation have relatively better catalytic performance, and the centrifugal conditions are 3500r for 2min. Since the water is not completely removed, the drying time is slower than that of filtration separation. Since the filter cake formed by filtration separation is directly dried, the drying time can be accelerated. However, the number of washing times needs to be controlled during filtration separation to avoid the loss of metal elements such as Gd and La.

[0017] The calcination in step (4) is carried out in a nitrogen atmosphere or an air atmosphere, wherein the morphology formed in the air atmosphere is a cage-type morphology.

[0018] The oxygen-carrying and catalytic dual-function particles prepared according to the preparation method are used to prepare light olefins by CO2 hydrogenation. The reaction conditions are H2 / CO2=1-4, 150-400℃, 2-4MPa, 1000-4000h -1 .

[0019] The oxygen carrier can also be modified by impregnation of elements such as Zr, Co, Mg, Mn, Na, Zn, and K to optimize the catalytic activity of the oxygen carrier. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The XRD patterns of samples 1-6 before reaction are shown in Figure 1. a: sample 1; b: sample 2; c: sample 3; d: sample 4; e: sample 5; f: sample 6.

[0021] Figure 2 The XRD patterns of samples 1-6 after reaction: a: sample 1; b: sample 2; c: sample 3; d: sample 4; e: sample 5; f: sample 6.

[0022] Figure 3 These are SEM images of samples 1 to 6. a: sample 1; b: sample 2; c: sample 3; d: sample 4; e: sample 5; f: sample 6.

[0023] Figure 4 The XPS spectra of Fe2p and Cu2p before reaction for samples 1-6 are shown below. (I) Fe2p; (II) Cu2p; a: sample 1; b: sample 2; c: sample 3; d: sample 4; e: sample 5; f: sample 6.

[0024] Figure 5 XPS spectra of Fe2p and Cu2p in samples 1-6 after reaction. (III): Fe2p; (IV): Cu2p. a: Sample 1; b: Sample 2; c: Sample 3; d: Sample 4; e: Sample 5; f: Sample 6.

[0025] Figure 6 This is a schematic diagram of the CO2 hydrogenation performance of catalysts prepared by Sample 7 and Sample 2.

[0026] Figure 7 Schematic diagram of CO2 hydrogenation performance of different potassium-modified catalysts: K / LaFeCuO3, K / GdLaFeCu0.25O3, K / GdLaFeCuO.5O3, K / GdLaFeCu0.75O3, and K / GdLaFeCuO3. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below through an implementation case. This implementation case is implemented based on the technology of the present invention. Detailed implementation methods and specific operating procedures are now given to illustrate the creativity of the present invention, but the protection scope of the present invention is not limited to the following implementation case.

[0028] Based on the information contained in this application, it will be readily apparent to those skilled in the art that various changes can be made to the precise description of the present invention without departing from the spirit and scope of the appended claims. It should be understood that the scope of the present invention is not limited to the defined processes, properties, or components, as these embodiments and other descriptions are provided merely to illustrate specific aspects of the present invention. In fact, various changes that a person skilled in the art or related fields would clearly be able to make to the embodiments of the present invention are encompassed within the scope of the appended claims.

[0029] For a better understanding of the present invention and not to limit the scope of the present invention, all numbers used in this application to express amounts, percentages, and other numerical values ​​should be understood as modified by the word "about" in all cases. Therefore, unless otherwise specified, the numerical parameters listed in the specification and the appended claims are approximate values, which may vary depending on the desired properties to be obtained. Each numerical parameter should at least be regarded as obtained based on the reported significant figures and by conventional rounding methods.

[0030] Example 1

[0031] Lanthanum nitrate, gadolinium nitrate, ferric nitrate, and copper nitrate were weighed and dissolved in deionized water in a stoichiometric ratio of Gd:Fe=1:1, Fe:Cu=1, and glucose:(La+Gd+Fe+Cu)=3. The mixture was stirred for 2 hours, then transferred to an autoclave and reacted at 180°C for 10 hours before cooling to room temperature. The black precipitate from the autoclave was centrifuged and washed with deionized water. The black powder was then dried in an 80°C oven for 12 hours and placed in a muffle furnace (under air atmosphere). The temperature was increased at 5°C / min to 400°C and held at that temperature for 1 hour. The temperature was then increased at 2°C / min to 750°C and held at that temperature for 5 hours. After cooling, the target catalyst sample was obtained by grinding. This is designated as Sample 1.

[0032] Example 2

[0033] Lanthanum nitrate, gadolinium nitrate, ferric nitrate, and copper nitrate were weighed and dissolved in deionized water in a stoichiometric ratio of La:Fe = 2:1, Fe:Cu = 1, and glucose:(La+Gd+Fe+Cu) = 3. The mixture was stirred for 2 hours, then transferred to an autoclave and reacted at 180°C for 10 hours before cooling to room temperature. The black precipitate from the autoclave was centrifuged and washed with deionized water. The black powder was then dried in an 80°C oven for 12 hours and placed in a muffle furnace (under air atmosphere). The temperature was increased at 5°C / min to 400°C and held at that temperature for 1 hour. The temperature was then increased at 2°C / min to 750°C and held at that temperature for 5 hours. After cooling, the target catalyst sample was obtained by grinding. This was designated as Sample 2.

[0034] Example 3

[0035] Lanthanum nitrate, gadolinium nitrate, iron nitrate, and copper nitrate were weighed and dissolved in deionized water in a stoichiometric ratio of La:Gd:Fe = 2:1:1, Fe:Cu = 0.25, and glucose:(La+Gd+Fe+Cu) = 3. The mixture was stirred for 2 hours, then transferred to an autoclave and reacted at 180°C for 10 hours before cooling to room temperature. The black precipitate from the autoclave was centrifuged and washed with deionized water. The black powder was then dried in an 80°C oven for 12 hours and placed in a muffle furnace (under air atmosphere). The temperature was increased at 5°C / min to 400°C and held at this temperature for 1 hour. The temperature was then increased at 2°C / min to 750°C and held at this temperature for 5 hours. After cooling, the target catalyst sample was obtained by grinding. This was designated as Sample 3.

[0036] Example 4

[0037] Lanthanum nitrate, gadolinium nitrate, iron nitrate, and copper nitrate were weighed and dissolved in deionized water in a stoichiometric ratio of La:Gd:Fe = 2:1:1, Fe:Cu = 0.5, and glucose:(La+Gd+Fe+Cu) = 3. The mixture was stirred for 2 hours, then transferred to an autoclave and reacted at 180°C for 10 hours before cooling to room temperature. The black precipitate from the autoclave was centrifuged and washed with deionized water. The black powder was then dried in an 80°C oven for 12 hours and placed in a muffle furnace (under air atmosphere). The temperature was increased at 5°C / min to 400°C and held at that temperature for 1 hour. The temperature was then increased at 2°C / min to 750°C and held at that temperature for 5 hours. After cooling, the target catalyst sample was obtained by grinding. This was designated as Sample 4.

[0038] Example 5

[0039] Lanthanum nitrate, gadolinium nitrate, iron nitrate, and copper nitrate were weighed and dissolved in deionized water in a stoichiometric ratio of La:Gd:Fe = 2:1:1, Fe:Cu = 0.75, and glucose:(La+Gd+Fe+Cu) = 3. The mixture was stirred for 2 hours, then transferred to an autoclave and reacted at 180°C for 10 hours before cooling to room temperature. The black precipitate from the autoclave was centrifuged and washed with deionized water. The black powder was then dried in an 80°C oven for 12 hours, then placed in a muffle furnace (under air atmosphere) and heated at 5°C / min to 400°C for 1 hour. The temperature was then increased to 750°C at 2°C / min and held at this temperature for 5 hours. After cooling and grinding, the target catalyst sample was obtained. The molar amount of Cu added was recorded as LaGdFeCuO3. This was designated as Sample 5.

[0040] Example 6

[0041] Lanthanum nitrate, gadolinium nitrate, iron nitrate, and copper nitrate were weighed and dissolved in deionized water in a stoichiometric ratio of La:Gd:Fe = 2:1:1, Fe:Cu = 1, and glucose:(La+Gd+Fe+Cu) = 3. The mixture was stirred for 2 hours, then transferred to an autoclave and reacted at 180°C for 10 hours before cooling to room temperature. The black precipitate from the autoclave was centrifuged and washed with deionized water. The black powder was then dried in an 80°C oven for 12 hours and placed in a muffle furnace (under a nitrogen atmosphere). The temperature was increased at 5°C / min to 400°C and held at that temperature for 1 hour. The temperature was then increased at 2°C / min to 750°C and held at that temperature for 5 hours. After cooling, the target catalyst sample was obtained by grinding. This was designated as Sample 6.

[0042] Example 7

[0043] LaFeCuO3 catalyst was prepared by sol-gel method. Lanthanum nitrate, iron nitrate, copper nitrate were weighed according to the stoichiometric ratio (La:Fe=2:1, Fe:Cu=1), and citric acid (1.5 times the total amount of metal ions) was used as a reaction complexing agent to obtain a precursor solution. After forming a gel in an 80°C water bath, it was placed in a 105°C drying oven and dried for 12 hours. Subsequently, the dried powder was ground and placed in a muffle furnace, and the temperature was increased to 400°C at a rate of 5°C / min and kept constant for 1 hour, then increased to 750°C at a rate of 2°C / min and kept constant for 5 hours. After cooling, the target catalyst sample was obtained by grinding. It was recorded as sample 7.

[0044] Catalyst performance testing and characterization:

[0045] In order to make the catalyst react better and avoid clogging the reaction tube, the catalysts prepared in Examples 1 to 11 of the present invention were all made into catalyst particles of 20 to 40 mesh.

[0046] The present invention uses a micro fixed bed reactor to evaluate the catalyst. The process conditions are as follows: 0.5-5 mL of 20-40 mesh catalyst, reaction temperature of 280-400°C, reaction pressure of 0.5-8 MPa, raw gas H2 / CO2=1 or 2, and space velocity of 500-5000·h -1 .

[0047] For example, the performance of the catalyst prepared in Example 1 was evaluated in a micro fixed bed reactor. The specific operation steps are as follows: 1.0 mL of the sample catalyst prepared in Example 1 was weighed and loaded into the constant temperature zone in the middle of the reaction tube. The feed gas was H2 / CO2=3, the temperature was 320°C, the pressure was 2.0 MPa, and the space velocity (GHSV) was 1000 h -1 After reaching a steady state, samples were collected and analyzed every 3 hours. Gas chromatography was used to quantitatively and qualitatively analyze the feed gas and products. The CO conversion rate and selectivity of each component were calculated using the methane correlation method described in "Determination of H2, N2, CO, CO2, and C1-C8 Hydrocarbons in Coal-based Fischer-Tropsch Synthesis Tail Gas by Gas Chromatography."

[0048] It can be seen that the prepared samples improve the CO2 conversion rate, and in the product distribution, the hydrocarbon products change significantly. The catalysts prepared in various examples of the present invention all show good CO2 hydrogenation performance.

[0049] Figure 1 is the X-ray diffraction pattern of different composite oxides. Figure 1 As can be seen in Figure b, except for the LaCuO3 phase, the other Gd-containing samples all mainly present the GdFeO3 phase. The results show that the catalysts prepared by the hydrothermal method are perovskite phases, indicating that the introduction of carbon does not affect the formation of the perovskite phase. For the La(Gd)Fe(Cu)O3 series ABO3 type catalysts, when there is no La at the A position and only Gd ( Figure 1), the sample retained the characteristic peak of GdFeO3, and a small amount of Gd2O3 phase was found, indicating that the amount of Gd could not fully meet the metal cations at the B site, and a small amount of Gd2O3 oxide peak appeared. When La and Gd coexisted at the A site, the sample did not show the characteristic peak of LaFeO3 phase, but the characteristic diffraction peaks of LaCuO3 and CuO were found. The characteristic peak of LaFeO3 phase may overlap with the characteristic peak of LaCuO3 phase, the characteristic diffraction peak of metal Fe oxide disappeared, the intensity of LaFeO3 diffraction peak was low, and the characteristic diffraction peak of LaFeO3 phase was not detected. The chemical potential of La is relatively low compared to Gd, and it is difficult to form metal composite oxide particles with Fe on the surface. Gd's strong electron pair supply ability forms the GdFeO3 phase, and the La element may be lost or highly dispersed in the perovskite system during the washing process. When La and Gd coexist at the A site, the sample mainly presents the GdFeO3 phase, and no characteristic diffraction peaks of Cu and Fe oxides are found. As Cu partially replaces Fe, the characteristic diffraction peak weakens, indicating that the introduction of Cu inhibits the growth of LaGdFeO3 crystallites, resulting in a decrease in the degree of crystallization. The XRD spectrum of the sample is an orthorhombic phase, which is in good agreement with the standard XRD data space group. As Gd partially replaces La, the exchange makes the formation of the iron oxide phase possible. Secondly, the Cu doping amount on the B site of the perovskite increases, and the peak signal of the Fe3O4 phase is enhanced during the reaction. Moreover, the position of the main diffraction peak has a tendency to move slightly to a higher diffraction angle. This effect is strongest in LaGdFeCuO3. This is because during the chlorination reaction, the carbon-coated perovskite structure promotes the formation of oxygen vacancies and the partial reduction of metallic Fe, resulting in the expansion of the unit cell. At the same time, affected by a smaller The cations are larger Cu 2+ cation As for the effect of substitution, an increase in crystallite size and a decrease in lattice strain were observed, further confirming the lattice expansion.

[0050] Figure 2 This is the XRD spectrum of the sample after hydrogenation. The GdFeO3 diffraction peak remains after the reaction, indicating that the crystal structure of the perovskite catalyst is not completely destroyed. Characteristic peaks of Fe2O3 and CuO appear in all samples after the reaction, indicating that the hydrothermal carbon-coated perovskite system has disrupted the inherent structural stability of perovskites. Due to the additional driving force of establishing the Fe-Cu stoichiometric balance in the perovskite structure, metal segregates from the lattice during the hydrogenation reaction, likely due to the dissolution of B-site cations. Figure 2Figure a shows the GdFeCuO3 sample after the reaction. It exhibits a rich variety of phases, including CuO, GdFeO3, Fe(CO3), Fe3O4, and Fe2O3. This suggests that the presence of Cu promotes the desolvation of Fe particles. During the hydrogenation reaction, the sample transforms into an iron phase that favors the formation of light olefins. It is speculated that CO2 activation cleaves CO bonds, and the resulting oxygen atoms diffuse into the perovskite matrix, activating the desolvated Fe active sites. CO* species then insert into the crystal lattice to form Fe(CO3). Figure 2 b shows the LaFeCuO3 sample after the reaction, in which LaCu2O4, CuO, Fe3O4, Fe2O3, and Fe phases appear. Due to the easy reduction of Cu, Cu preferentially dissolves at a lower temperature, and the formation of additional metallic CuO phase can be observed. u It is easy to reduce, and the perovskite structure stability of the sample is relatively poor. Figure 2 The sample cf still retains the GdFeO3 phase, and CuO, Fe3O4, and Fe2O3 phases are found. During the reaction, there is an oxidation process of FeO, which causes a phase change to appear Fe3O4. Compared with the GdFeCuO3 sample, the characteristic diffraction peak has a clear peak shape and a weak diffraction peak intensity. With the increase of the amount of Cu, the diffraction peak intensity increases, and an iron oxide phase evolves during the hydrogenation reaction. When there are more than two B-site metals, the phase change is complex, especially after the introduction of Gd. These results show that the doping of Cu enhances the metal dissolution process and also makes the active metal elements prone to phase change in the CO2 hydrogenation reaction atmosphere, including reduction to a zero-valent metal state (such as Fe 0 The appearance of Cu is not completely reduced and is in an oxidized state. It is speculated that it participates in the reaction with iron oxides in the CO2 hydrogenation reaction and plays a good synergistic role. Combined with the analysis of the CO2 hydrogenation catalytic activity evaluation data, the carbon-coated Fe-based perovskite promotes the dissolution of metal Fe, and the Fe3O4, Fe2O3, and Fe(CO3) formed in the reaction improve the CO2 hydrogenation catalytic activity. Different Cu-doped catalysts show similar Fe phase changes, which are formed by the interaction of the metal Fe and Cu particles that have been desolvated during the CO2 hydrogenation process. With the increase of Cu doping amount, the activity of LaGdFeCuO3 shows a trend of first high and then low. These results show that the surface chemical properties of perovskite are rich, and the change of the catalyst surface to the reaction chemical potential promotes the increase of substate metal ions and segregation effect, which in turn affects the CO2 hydrogenation catalytic activity.

[0051] Figure 3SEM images of samples 1-6 are shown. As can be seen from the images, the catalysts exhibit branched chains. These synthesized compounds exhibit similar morphology, tightly bound together, exhibiting a cage-like morphology and a porous, grid-like structure with no agglomeration. Increasing the Cu content results in some pore ablation and damage, increasing the overall roughness and irregular morphology. This wrinkled surface increases the effective collision area between the catalyst surface and reactants, while also increasing the number of active sites, thereby promoting the reaction process. As the Cu content increases, a small portion of the cage-like morphology becomes rougher. The cage-like morphology provides structural confinement for the reaction and ensures the instability of the non-covalently modified surface, thereby releasing iron oxides and other molecules. Covalent bonds between the metal and carbon interact, while the metal oxide molecules are encapsulated within the carbon. Under hydrothermal conditions, the molecular building blocks of carbon groups and hydroxyl groups guide the catalyst's growth primarily in the lateral direction, leading to self-assembly into hollow spheres. This structure facilitates tailoring of the catalyst's surface properties in a non-covalent and modular manner. The cross-linked structure helps expose more unsaturated active sites within the material, thereby enhancing catalytic activity.

[0052] During the hydrothermal preparation process, the catalyst is formed by covalent bonding between the particle units along a specific direction. However, in the unique perovskite crystal structure, reversible non-covalent bonds occur in the lateral direction, forming interconnected, closed hollow cage-like spheres. This self-assembly process, constrained by the hydrothermal conditions, tends to reduce the free energy of the system during equilibrium. The formation of Fe nanoparticles can explain the higher catalytic activity of Cu-doped catalysts compared to undoped catalysts.

[0053] In order to determine the surface composition and valence state of the elements, XPS analysis was performed on the samples before and after the reaction. Figure 4 Fe2p before and after perovskite reaction 3 / 2 、Cu2p 3 / 2 XPS spectrum. From Figure I and Figure III, it can be seen that the Fe2p peaks are concentrated at 709-711eV and 722-724eV. ​​This is attributed to Fe 3+ Characteristic peaks. In Figure I, samples b, c, d, e, and f have small peaks between 717 ± 0.4 eV, which are attributed to the α-Fe2O3 satellite peak. In Figure III, Fe(2p 32 ) moves slightly toward the lower binding energy direction. The curves of samples b, c, d, e, and f are relatively flat between 717±0.4eV, indicating that the α-Fe2O3 satellite peak disappears, indicating that the α-Fe2O3 phase is converted into Fe3O4 after the reaction, which is consistent with the XRD results. CO2 activation usually occurs on iron oxides. XPS and XRD confirm the existence of the Fe3O4 phase, which will be beneficial to the reverse water gas reaction and FT reaction, and will promote the reaction and CH x increase.

[0054] Figure 5 The XPS spectra of Fe2p and Cu2p of the sample after reaction are shown in Figure II and Figure IV. The changes of Cu2p before and after reaction are obvious. The peaks of Cu2p before and after reaction are obviously different. 3 / 2 The main peak (933.5eV) and the spin-orbit contribution of Cu2p 1 / 2 (954eV), there are also corresponding satellite peaks located at 941eV and 961eV. Combined with XRD analysis, the Cu-doped perovskite becomes unstable during the CO2 hydrogenation activation process, and Cu + 、Cu 0 During the hydrogenation process, Cu participates in the redox process of the reaction, and the final surface accumulation is mostly Cu 2+ ion.

[0055] Figure 6 The CO2 hydrogenation performance of the catalysts prepared by the sol-gel method (sample 7) and the hydrothermal method (sample 2) is shown. By comparison, the LaFeCuO3 catalyst prepared by the hydrothermal method has good performance in producing light olefins. The CO2 conversion rate of the carbon-coated LaFeCuO3 catalyst is 17.51%, CH4 accounts for 41.36% of the total hydrocarbon distribution, and C5 + The carbon-coated catalyst effectively carried out the RWGS-FT reaction, and the CO selectivity was reduced from 62.26% to 41.37%, and the light olefin C2 ＝ -C4 ＝The catalyst's activity increased from 27.21% to 36.33%. Combined with XRD spectra before and after the reaction, the hydrothermally prepared catalyst exhibited an iron oxide phase, promoting the CO2 hydrogenation reaction at the iron metal active site. The figure clearly shows that the partial exchange of Gd and La enhanced the catalytic activity, while the doping of Fe and Cu further enhanced the catalytic activity at the perovskite B site. The co-doped catalyst exhibited the best performance, indicating that co-doping is highly beneficial for the RWGS-FT reaction. The catalyst surface was enriched with Gd, La, Fe, and Cu ions, as well as a large number of oxygen vacancies, which are beneficial for the CO2 hydrogenation to olefins reaction. The Fe oxide particles formed by desolvation during the CO2 hydrogenation process affected the catalytic reaction process, and a decrease in catalytic activity with increasing Cu content was observed. This difference in catalytic activity provides evidence for the support-metal catalytic effect generated by the solid perovskite matrix and the desolvated metal. Combined with the phase evolution of Fe nanoparticles, Fe-based perovskites are more likely to overflow with increasing Cu content during the subsequent hydrogenation process. The increase in B-site oxygen vacancies promotes the filling of O from CO2 and the migration of lattice oxygen, thereby improving hydrocarbon formation performance. Combined with XRD, it is believed that the high catalytic activity of Cu and Fe co-doped perovskites is closely related to the desolvation of Fe nanoparticles, and it also reflects that the preparation method has a significant impact on the performance of the catalyst material. The perovskite catalyst modified with desolvated Fe oxide nanoparticles exhibits reversible and stable catalytic behavior.

[0056] Through A-site modification and B-site doping, the carbon-coated LaGdFeCuO3 perovskite catalyst grown in situ by hydrothermal method has good performance in CO2 hydrogenation to olefins. While the hydrothermal method retains the main skeleton of the perovskite, it also breaks the stability of the main lattice and promotes the infiltration of Fe from the lattice. The regulation of the Cu ratio can achieve the infiltration rate of the Fe content, produce lattice distortion and promote the formation of substate metal ions. Small-sized, highly active metal oxide particles are precipitated in a reducing reaction atmosphere. The metal oxide is embedded in the inner and outer surfaces of the LaGdFeCuO3 perovskite cage morphology in the form of anchors, showing a rich Fe 3 , Fe 2+ , Cu + , Cu 2+ ions, showing excellent CO2 hydrogenation catalytic performance and good anti-sintering performance.

[0057] Depend on Figure 7 It can be seen that after Gd element replaces part of La, C2 ＝ -C4 ＝ The olefin content increased significantly from 36.33 wt% to 44.72 wt%. With the change of Cu content, when the molar ratio of Fe:Cu≤0.75, C2 ＝ -C4 ＝Olefins account for 44 wt% of the total hydrocarbon distribution, and the selectivity of CH4 and CO does not change significantly with Cu. When Fe:Cu=1, the proportion of olefins decreases by 10%. It is speculated that the amount of active metals such as Cu that are reduced and exposed increases, which promotes the secondary hydrogenation reaction of olefins, which is mutually confirmed by the increase in CO2 conversion rate. Overall, Gd has a promoting effect on olefin formation. As the Cu content cannot be confined to the lattice, it has a positive effect on hydrogen adsorption and CO2 activation when exposed from the system. However, with the increase of Cu content, the O / P value decreases. This is due to the different electronic behaviors of the prepared catalysts, which show differences in catalytic performance. The Fe and Cu surfaces that migrated out of the lattice have a strong adsorption force for H2, which promotes the further hydrogenation of olefins to produce alkane products, resulting in a decrease in olefin selectivity. Gd partially replaces La, and Cu partially replaces Fe, resulting in oxygen vacancies (ABO) in the crystal structure. 3-δ ), which promotes oxygen migration, resulting in an increase in the lattice energy of the perovskite oxide and the activation of lattice oxygen. Due to the oxygen concentration gradient between the perovskite oxide and the environment, some active lattice oxygen elements will migrate to the crystal surface and escape into the atmosphere with low oxygen partial pressure, resulting in the formation of oxygen vacancies. The surface with fewer oxygen vacancies adsorbs O intermediates too strongly, resulting in a larger energy barrier for CO2 hydrogenation, while the surface with more oxygen vacancies has a weaker binding ability for oxygen, which is not conducive to the activation and hydrogenation of CO2. Combined with XPS and XRD characterization, the cage-type morphology of the perovskite changes the valence energy and binding energy of the elements. During the formation of oxygen vacancies, the loss of single electrons leads to the formation of electron holes in the perovskite oxide, which further promotes the coupling of CC bonds and CH bonds, thereby improving the catalytic performance of CO2 hydrogenation.

Claims

1. A method for preparing oxygen-carrying-catalytic dual-function particles, characterized in that The process includes the following steps: (1) Weigh La:Gd:Fe=1-3:1:1, Fe:Cu=0.1-0.75, glucose:(La+Gd+Fe+Cu)=3 in molar ratio. Dissolve in water, stir until uniform, and then transfer to the autoclave; (2) Place the reactor in an oven at 160-180°C for 8-12 hours, then cool to room temperature; (3) Separate the black precipitate from the reactor and wash it with deionized water; then dry the precipitate in an oven at 80°C; (4) After drying, the sample is placed in a muffle furnace for calcination, and then ground after cooling to obtain the target particles.

2. The method for preparing oxygen-carrying-catalytic dual-function particles according to claim 1, characterized in that The metal ions are derived from lanthanum nitrate, gadolinium nitrate, iron nitrate, and copper nitrate.

3. The method for preparing oxygen-carrying-catalytic dual-function particles according to claim 1, characterized in that The separation in step (3) is centrifugal separation.

4. The method for preparing oxygen-carrying-catalytic dual-function particles according to claim 1, characterized in that In step (4), the calcination is carried out in an air atmosphere under the conditions of heating to 400°C at a rate of 5°C / min and holding the temperature for 1 h, then heating to 750°C at a rate of 2°C / min and holding the temperature for 5 h.

5. The oxygen-carrying and catalytic dual-function particles prepared by the preparation method of claim 1 are used for hydrogenation of CO2 to produce light olefins, the reaction conditions being H2 / CO2 = 1-4, 150-400°C, 2-4 MPa, 1000-4000 h -1 .

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