Application of a ZnFeGaO4 spinel oxide in the carbon dioxide hydrogenation reaction

Abstract

The application discloses application of ZnFeGaO4 spinel oxide in a carbon dioxide hydrogenation reaction and belongs to the technical field of catalysts. 2+ The method realizes flexible switching of a reaction path in the same catalyst system, and the catalyst has excellent catalytic activity and structural stability, and the application provides a novel strategy for designing a high-efficiency and high-selectivity carbon dioxide conversion catalyst.

Description

Technical Field

[0001] This invention belongs to the fields of catalyst technology and energy chemical engineering, specifically relating to a ZnFeGaO4 spinel oxide and its application in the carbon dioxide hydrogenation reaction. Background Technology

[0002] With the acceleration of global industrialization, the concentration of CO2 in the atmosphere continues to rise, and the resulting greenhouse effect has become a major survival challenge. CO2 catalytic hydrogenation technology, especially the use of "green hydrogen" generated from renewable energy to convert CO2 into high-value products such as methanol, olefins, aromatics, and long-chain hydrocarbons, has attracted widespread attention. The core of this technology lies in the design and creation of catalysts.

[0003] Spinel oxides (AB₂O₄) have shown great potential in CO₂ hydrogenation. Current research largely focuses on single-metal or bimetallic systems, but existing catalysts still face a series of key challenges: some catalysts undergo irreversible spinel structure destruction under hydrogen pretreatment conditions, leading to phase separation and metal species aggregation, thus losing selectivity for methanol synthesis; methanol selectivity decreases significantly at high temperatures, with the reverse water-gas shift reaction dominating and CO becoming the main product; many catalysts exhibit low CO₂ conversion rates, and even with high methanol selectivity, their space-time yields remain limited; different metal oxides have uneven activation abilities for H₂ and CO₂, making it difficult to synergistically promote the target reaction pathway; and the reaction pathway is difficult to control, easily leading to CO generation via the carboxyl pathway or further hydrogenation to methane and C₂. 2+ The production of hydrocarbon byproducts increases significantly, especially when carbide phases such as Fe3C2 are formed. The catalyst is structurally unstable and its performance degrades significantly under changes in reaction atmosphere and reaction time.

[0004] More importantly, existing technologies struggle to achieve flexible switching between CO2 hydrogenation reaction pathways (methanol pathway and Fischer-Tropsch pathway) within the same catalyst system through simple and controllable pretreatment methods. The active phase structure of the catalyst strongly depends on the precursor composition and the external pretreatment atmosphere, but current preparation strategies lack a systematic design and application of this "composition-atmosphere-active phase-product" structure-activity relationship. Summary of the Invention

[0005] To address the problem of limited flexibility in controlling the reaction pathway in existing CO2 hydrogenation catalysts, this invention provides a method for precisely constructing active phase ZnFeGaO4 spinel oxides by adjusting the Fe content and pretreatment atmosphere, and its application in the CO2 hydrogenation reaction. The method of this invention synthesizes ZnFeGaO4 spinel precursors with different Fe contents via co-precipitation and pretreatment with different atmospheres to induce the in-situ formation of differentiated active phase structures (such as Fe@(Zn,Ga)O). x Interface or FeCx Carbides), thereby enabling precise guidance of the CO2 hydrogenation reaction pathway; directly applying the prepared catalyst to the CO2 hydrogenation reaction can significantly improve CO2 conversion and target products (such as methanol, low-carbon olefins, or C2C4). 5+ Selectivity of hydrocarbons.

[0006] In this invention, ZnFeGaO4 spinel oxide is prepared by a co-precipitation method. Specifically, Zn salt, Fe salt, and Ga salt are dissolved in deionized water, mixed, and then the mixed salt solution is added to the precipitant at 55-65°C with stirring. The pH of the mixture is adjusted to 9-10, and the mixture is stirred and aged for 2-4 hours. The solid and liquid are separated, the solid is washed until neutral, dried, and calcined to obtain ZnFeGaO4 spinel oxide. The molar ratio of Zn:Fe:Ga is 1:(1~2):1, the precipitant is 0.05-0.15g / mL ammonium carbonate solution, and the calcination temperature is 750~800℃.

[0007] The obtained ZnFeGaO4 spinel oxide was pretreated at 350-450℃ for 1-3 hours in a weak reducing atmosphere or an inert atmosphere before being used to prepare methanol by carbon dioxide hydrogenation reaction. The weak reducing atmosphere was N2 atmosphere containing 5-15% H2 by volume, and the inert atmosphere was nitrogen or argon. ZnFeGaO4 spinel oxide was pretreated in a syngas atmosphere at 350-450℃ for 1-3 hours, and then used in the carbon dioxide hydrogenation reaction to prepare C. 2+ Hydrocarbons are obtained by mixing the synthesis gas atmosphere H2 and CO in a volume ratio of (1~2):1.

[0008] The ZnFeGaO4 spinel oxide prepared by this invention, after being loaded with Na by an equal-volume impregnation method, and then pretreated at 350-450℃ for 1-3 hours in a weak reducing atmosphere, an inert atmosphere, or a syngas atmosphere, can be used for the preparation of C by carbon dioxide hydrogenation reaction. 2+ Hydrocarbons.

[0009] By selecting different pretreatment atmospheres, the product distribution can be flexibly controlled: in 5~15% H2 / N2, the material may be partially reduced, tending to form active sites with high selectivity for methanol synthesis, thereby guiding the reaction through the methanol intermediate pathway; in a CO / H2 mixture, the strong reducing power and moderate carbonizing ability of the atmosphere may promote deep reduction and carbonization of the material, forming a typical Fischer-Tropsch synthesis active phase, guiding the reaction through the low-carbon olefin intermediate pathway; while in an inert atmosphere, the material structure may remain relatively stable or undergo slight changes, and the reaction proceeds through the methanol intermediate pathway.

[0010] The present invention has the following beneficial effects: 1. A novel ternary spinel catalyst precursor is provided: for the first time, three active components, Fe, Zn and Ga, are integrated into a single spinel lattice of ZnFeGaO4. By precisely controlling the Fe content, the lattice parameters, cation occupancy and reduction behavior of the material can be systematically changed, providing a new platform for constructing a multifunctional synergistic catalytic interface. 2. Precise induction and switching of reaction pathways: By simply changing the reducing atmosphere (weakly reducing 10% H2 / N2, carbonizing synthesis gas, inert N2), the ZnFeGaO4 precursor can be induced to transform in situ into a completely different active phase (methanol synthesis active phase or Fischer-Tropsch synthesis active phase). This allows for flexible guidance of the CO2 hydrogenation reaction via the methanol intermediate pathway or the low-carbon olefin intermediate pathway, achieving targeted control from methanol to hydrocarbon products. This breaks the limitation of traditional catalysts with a single reaction pathway. 3. Balancing high catalytic activity and high structural stability: The in-situ precipitated active nanoparticles are anchored on the derived oxide matrix, forming a stable metal-support interaction that inhibits the aggregation and loss of active components. Simultaneously, the introduction of Ga enhances the catalyst's resistance to carbon deposition and its structural stability. The catalyst exhibits excellent catalytic stability during long-term operation. 4. Simple and efficient preparation process: The co-precipitation method for preparing spinel precursors is a mature process that is easy to scale up. The active phase can be constructed with only simple pretreatment in different atmospheres. Compared with complex multi-step impregnation or modification methods, it has greater prospects for industrial application. Attached Figure Description

[0011] Figure 1 X-ray diffraction (XRD) patterns of Zn1Fe1Ga1O4 and Zn1Fe2Ga1O4 spinel oxides; Figure 2 The images are scanning electron microscope (SEM) images of the Zn1Fe1Ga1O4 catalyst. Figure (a) shows the TEM images at different magnifications, and Figure (b) shows the EDX elemental distribution of C, Zn, Fe, and Ga. Figure 3 Images of the Zn1Fe1Ga1O4 catalyst (left image) and high-resolution transmission electron microscope (right image). Figure 4 XRD patterns of the catalysts after 12 hours of reaction under different pretreatment atmospheres; Figure 5 The CO2 hydrogenation reaction performance of Zn1Fe1Ga1O4 spinel oxide (left figure) or Na-Zn1Fe1Ga1O4 (right figure) under different pretreatment atmospheres; Figure 6 Zn1Fe with different Fe contents x Ga1O4 or Na-Zn1Fex Performance diagram of CO2 hydrogenation reaction of Ga1O4. Detailed Implementation

[0012] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the present invention is not limited to the following technical solutions. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field. Those skilled in the art can implement the invention by referring to various commonly used reference books, scientific and technological documents, or related instructions and manuals prior to the filing date of this invention; Example 1: Preparation and application of ZnFeGaO4 spinel oxide 1. Weigh out Zn(NO3)2·6H2O, Fe(NO3)3·9H2O and Ga(NO3)3·xH2O according to the molar ratios of Zn:Fe:Ga of 1:1:1 and 1:2:1 respectively, and dissolve them in deionized water. Under the conditions of a 60℃ water bath and vigorous stirring, add the mixed salt solution dropwise to a 0.1 g / mL ammonium carbonate solution. After mixing, adjust the pH to 9.5 with ammonia water, continue stirring and aging for 3 hours, filter, wash the solid with deionized water until neutral, dry it in an 80℃ oven for 12 hours, and then calcine it in a muffle furnace at a temperature of 3℃ / min to 800℃ for 4 hours. After natural cooling, obtain Zn1Fe1Ga1O4 (Zn:Fe:Ga=1:1:1) and Zn1Fe2Ga1O4 (Zn:Fe:Ga=1:2:1) spinel powders; The obtained samples were characterized by XRD. Figure 1 The results showed clear spinel characteristic diffraction peaks, and with increasing Fe content, weak iron oxide diffraction peaks appeared.

[0013] SEM image of Zn1Fe1Ga1O4 ( Figure 2 The catalyst surface exhibits a "coral" morphology; TEM and HRTEM images ( Figure 3 The fresh particles are uniform in size, with clear lattice stripes and a spacing of about 0.26 nm, corresponding to the spinel (331) crystal plane. No metal or carbide nanoparticles were found to precipitate.

[0014] 2. Effects of different pretreatments on atmospheric catalytic performance 0.2 g of Zn1Fe1Ga1O4 spinel oxide powder was packed into a stainless steel tubular reactor, and three different pretreatment atmospheres were introduced at a flow rate of 30 mL / min: N2 containing 10% H2, H2 / CO (volume ratio 1:1), and N2. The reactor was then activated in situ at 400 °C for 2 hours. Subsequently, the temperature was lowered to 320 °C, and a reaction mixture (73% H2, 24% CO2, 3% Ar) was introduced, while the pressure was increased to 4.0 MPa and the space velocity was controlled at 4500 mL·g.-1 ·h -1 The products were analyzed using an online gas chromatograph.

[0015] The catalyst was characterized by XRD after 12 hours of pretreatment in three different pretreatment atmospheres. Figure 4 The results showed that after N2 pretreatment with 10% H2, weak diffraction peaks of metallic Fe or FeZn alloy appeared; after H2 / CO pretreatment, characteristic peaks of carbides belonging to Fe5C2 or Fe3C appeared; and after N2 pretreatment, the spinel structure was still maintained.

[0016] Figure 5 The results in the left figure show that the catalyst (Zn1Fe1Ga1O4) pretreated with N2 containing 10% H2 has a CO2 conversion rate of 7.9%, a methanol selectivity of 81.7%, and a hydrocarbon selectivity of about 5%, with the reaction pathway being the methanol intermediate pathway.

[0017] The catalyst (Zn1Fe1Ga1O4) pretreated with N2 has a CO2 conversion rate of 6.5%, a methanol selectivity of 90.1%, and a hydrocarbon selectivity of about 1%. The reaction pathway is the methanol intermediate pathway.

[0018] The catalyst (Zn1Fe1Ga1O4) pretreated with H2 / CO achieved a CO2 conversion rate of 26.6%. Selectivity 10.6%, C 5+ Selectivity was 8.9%, CH4 selectivity was 51.2%, and the reaction pathway was the Fischer-Tropsch synthesis pathway.

[0019] The above results demonstrate that the CO2 hydrogenation pathway can be precisely controlled on the same catalyst simply by changing the pretreatment gas atmosphere.

[0020] 3. Effect of different Fe contents on catalytic performance Using the same reaction conditions as in step 2, the performance of Zn1Fe1Ga1O4 and Zn1Fe2Ga1O4 was compared, and the results are as follows: Figure 6As shown; under a N2 pretreatment atmosphere, the CO2 conversion rate increased from 6.5% to 10.0%, the methane selectivity increased significantly from 8.9% to 70.4%, while the methanol selectivity decreased sharply from 90.1% to 15.6%, with small amounts of C2-C4 alkanes (2.1%) and alkenes (0.9%) generated; under a N2 pretreatment atmosphere containing 10% H2, the CO2 conversion rate increased from 7.9% to 11.5%, the methane selectivity increased from 13.3% to 78.2%, and the methanol selectivity decreased from 81.7% to 7.7%; under a CO / H2 reaction atmosphere, the CO2 conversion rate remained basically the same (26.6% vs. 26.3%), the methane selectivity decreased slightly to 49.4%, and the C2–C4 alkanes and alkenes increased from 28.7% and 10.6% to 29.6% and 11.4%, respectively. 5+ Selectivity remained largely unchanged (8.9% vs. 8.8%).

[0021] Therefore, increasing the Fe content generally improves CO2 conversion under Na-free conditions (especially in N2 atmosphere with 10% H2), but strongly inhibits methanol formation and promotes methanation; it slightly promotes C2-C4 hydrocarbons under CO / H2 atmosphere, but only slightly promotes C4 hydrocarbons. 5+ The impact is not significant.

[0022] Example 2: Preparation and Catalytic Performance Experiment of Na-Supported ZnFeGaO4 Spinel Oxide 1. Using the equal-volume impregnation method, 0.5 g of Zn1Fe1Ga1O4 or Zn1Fe2Ga1O4 spinel oxide was mixed in 0.954 mL of 0.092 g / mL sodium nitrate solution, 3 mL of anhydrous ethanol was added, and the mixture was ground in a mortar. After aging for 3 hours, the mixture was dried in an oven at 80℃ for 12 hours, and then calcined in a tube furnace at 400℃ for 3 hours under an Ar atmosphere at a rate of 3℃ / min. The mixture was then allowed to cool naturally to obtain catalysts Na-Zn1Fe1Ga1O4 and Na-Zn1Fe2Ga1O4. 2. Referring to step 2 of Example 1, the catalyst Na-Zn1Fe1Ga1O4 was activated in situ at 400°C for 2 hours under three different pretreatment atmospheres; then it was used for the carbon dioxide hydrogenation reaction. See results Figure 5 The right figure shows that the catalyst loaded with Na catalyzes the hydrogenation of carbon dioxide, and the product obtained is C. 2+ Hydrocarbons, reacted via the Fischer-Tropsch synthesis pathway; The Na-Zn1Fe1Ga1O4 catalyst pretreated with N2 achieved a CO2 conversion rate of 25.3%. Selectivity 42.4%, C 5+ Selectivity 24.8%, CH4 selectivity 25.2%; The Na-Zn1Fe1Ga1O4 catalyst pretreated with N2 containing 10% H2 achieved a CO2 conversion rate of 28.9%. Selectivity 39.5%, C 5+ Selectivity 33%, CH4 selectivity 18.6%; The Na-Zn1Fe1Ga1O4 catalyst pretreated with H2 / CO achieved a CO2 conversion rate of 37.1%. Selectivity 43%, C 5+ Selectivity was 34%, and CH4 selectivity was 17.7%.

[0023] 3. Effect of different Fe contents on catalytic performance The method is the same as above, and the results are shown below. Figure 6 With increasing the Fe content, the CO2 conversion rate of the catalyst showed an increasing trend under N2, H2, and CO / H2 atmospheres, increasing from 25.3%, 28.9%, and 37.1% to 33.7%, 29.5%, and 41.7%, respectively. Meanwhile, CO selectivity decreased significantly under all atmospheres, from 35.1%, 23.1%, and 9.9% to 18.6%, 17.9%, and 7.7%, respectively. This indicates that increasing the Fe content is beneficial for suppressing the reverse water-gas shift side reaction and promoting the directional conversion of CO2 into hydrocarbon products.

[0024] Regarding product distribution, under hydrogen-containing atmospheres (H2, CO / H2), the selectivity for CH4 decreased slightly, while that for C... 5+ The selectivity for long-chain hydrocarbons was slightly improved, while the selectivity for C2-C4 olefins generally decreased, and the selectivity for C2-C4 alkanes increased accordingly. This indicates that the increase in Fe content enhanced the hydrogenation capacity and carbon chain growth capacity of the catalyst, while also promoting the secondary hydrogenation saturation of olefins.

Claims

1. An application of a ZnFeGaO4 spinel oxide in the hydrogenation reaction of carbon dioxide; The ZnFeGaO4 spinel oxide is obtained by dissolving Zn salt, Fe salt, and Ga salt in deionized water, mixing them, adding the mixed salt solution to a precipitant at 55-65℃ with stirring, adjusting the pH of the mixture to 9-10, continuing stirring and aging for 2-4 hours, separating the solid and liquid, washing the solid until neutral, drying, and calcining. ZnFeGaO4 spinel oxide is pretreated in a weak reducing atmosphere or an inert atmosphere at 350-450℃ for 1-3 hours and then used to prepare methanol by carbon dioxide hydrogenation. ZnFeGaO4 spinel oxide, after pretreatment in a syngas atmosphere at 350-450℃ for 1-3 hours, is used to prepare C by carbon dioxide hydrogenation. 2+ Hydrocarbons.

2. The application according to claim 1, characterized in that: The molar ratio of Zn:Fe:Ga is 1:(1~2):

1.

3. The application according to claim 1, characterized in that: The precipitant is a 0.05-0.15 g / mL ammonium carbonate solution.

4. The application according to claim 1, characterized in that: The calcination temperature is 750~800℃.

5. The application according to claim 1, characterized in that: The weak reducing atmosphere is a N2 atmosphere containing 5-15% H2 by volume.

6. The application according to claim 1, characterized in that: The inert atmosphere is nitrogen or argon.

7. The application according to claim 1, characterized in that: Syngas atmosphere H2 and CO are mixed in a volume ratio of (1~2):

1.

8. The application according to claim 1, characterized in that: ZnFeGaO4 spinel oxide, after being loaded with Na using an equal-volume impregnation method, is pretreated for 1-3 hours at 350-450℃ under a weak reducing atmosphere, an inert atmosphere, or a syngas atmosphere, and then used in the carbon dioxide hydrogenation reaction to prepare C. 2+ Hydrocarbons.

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