Preparation method of indium oxide-based nanoparticle superstructure catalyst

Abstract

The invention provides a preparation method of an indium oxide-based nanoparticle superstructure catalyst, and relates to the technical field of catalyst preparation. In the process of preparing the In-MIL-68 crystal, a transition metal oxide precursor and a transition metal dopant are added to form the transition metal oxide and transition metal co-doped In-MIL-68 crystal, and then the transition metal oxide and transition metal co-doped In-MIL-68 crystal is calcined to obtain the transition metal oxide and transition metal co-doped In-MIL-68 crystal. According to the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube and the preparation method thereof, an In2O3-transition metal oxide interface nanotube skeleton structure is prepared by adopting an MOF template method, a heterogeneous interface synergistic system is constructed, and meanwhile, the transition metal ions are introduced for doping, so that the oxygen vacancy and the interface electronic state can be regulated and controlled, and the performance of the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube is improved. The catalytic performance is improved, and carbon dioxide activation is enhanced.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation technology, and in particular to a method for preparing an indium oxide-based nanoparticle superstructure catalyst. Background Technology

[0002] In methanol synthesis, while low-temperature conditions (<200℃) help suppress reverse water-gas shift side reactions (RWGS), they also lead to excessively low kinetic rates. Conversely, high-temperature environments (>250℃), while improving reaction efficiency, exacerbate catalyst sintering deactivation and reduced selectivity. Existing copper-based and palladium-based catalysts generally face bottlenecks such as poor resistance to sintering and high dependence on precious metals. In particular, they are prone to active component migration or structural collapse during continuous operation, making it difficult to meet the long-term stability requirements of industrial plants.

[0003] Indium oxide (In₂O₃) has become a research hotspot in the field of catalysis in recent years due to its unique oxygen vacancy activation mechanism and excellent anti-sintering properties. However, its single-component structure still faces many challenges, such as insufficient active site density, weak conductivity and electron mobility, and limited reduction capacity. Traditional modification strategies, such as noble metal loading or composite with a support, have suppressed sintering to some extent, but they are often accompanied by new problems such as interfacial stress cracking and electron localization, which limit further improvement in catalytic performance.

[0004] In existing technologies, In(NO3)3·xH2O and terephthalic acid are typically dissolved in DMF solvent to obtain In-MIL-68, which is then transferred to a muffle furnace for calcination to obtain In2O3 nanotubes with a hollow tubular morphology. The catalytic activity of the hollow tubular In2O3 nanotubes obtained by this method is not very good; therefore, there is an urgent need to design an In2O3 superstructure nanotube with better catalytic activity. Summary of the Invention

[0005] One objective of this invention is to provide a method for preparing indium oxide-based nanoparticle superstructure catalysts, thereby solving the technical problem of poor catalytic activity of hollow tubular In2O3 nanotubes.

[0006] A further objective of this invention is to improve the thermocatalytic stability of In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes.

[0007] In particular, the present invention provides a method for preparing an indium oxide-based nanoparticle superstructure catalyst, comprising the following steps: Dissolve In(NO3)3·xH2O and terephthalic acid in N,N-dimethylformamide to obtain a first mixed solution, wherein the concentration of In(NO3)3 in the first mixed solution is any value between 0.8 mg / ml and 1.7 mg / ml, and the concentration of terephthalic acid is any value between 0.8 mg / ml and 1.7 mg / ml; A transition metal oxide precursor and a transition metal dopant are added to the first mixed solution and stirred until dissolved to obtain a second mixed solution. The concentration of the transition metal oxide precursor in the second mixed solution is any value between 0.35 mg / ml and 0.8 mg / ml, and the concentration of the transition metal dopant is any value between 0.03 mg / ml and 0.25 mg / ml. The first transition metal in the transition metal oxide precursor is different from the second transition metal in the transition metal dopant. The second mixed solution was transferred to a reaction vessel and heated to 120℃-150℃ for 12h-24h to obtain In-MIL-68 crystals co-doped with transition metal oxides and transition metals. The In-MIL-68 crystal, co-doped with the transition metal oxide and the transition metal, was transferred to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doped, wherein the second transition metal was doped within the In2O3 lattice.

[0008] Specifically, the transition metal oxide precursor is ZrOCl2·8H2O, and the transition metal dopant is one of Fe(NO3)3·9H2O, Ni(NO)3·6H2O, Pb(NO3)2, and Sn(NO3)4; The transition metal oxide and the transition metal co-doped In-MIL-68 crystal are ZrO2 and the second transition metal co-doped In-MIL-68 crystals.

[0009] Specifically, the transition metal oxide precursor is Ce(NO3)3·6H2O, and the transition metal dopant is one of Fe(NO3)3·9H2O, Ni(NO)3·6H2O, Pb(NO3)2, and Sn(NO3)4; The transition metal oxide and the transition metal co-doped In-MIL-68 crystal are CeO2 and the second transition metal co-doped In-MIL-68 crystals.

[0010] Specifically, the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is transferred to a muffle furnace for calcination to obtain a composite superstructured nanotube of In2O3-transition metal oxide-transition metal co-doped, wherein the second transition metal is doped within the In2O3 lattice, the process further includes the following steps: The In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes were immersed in a mixed solution of the transition metal dopant and a polar organic solvent that is miscible with water and has coordination ability, and stirred for 1-3 hours. The In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes were dried after soaking and then calcined again to obtain the doped In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes.

[0011] Specifically, the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is transferred to a muffle furnace for calcination to obtain a composite superstructured nanotube of In2O3-transition metal oxide-transition metal co-doped, wherein the second transition metal is doped within the In2O3 lattice, the process further includes the following steps: The In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes were subjected to plasma reduction treatment or ultraviolet-assisted reduction treatment.

[0012] Specifically, the step of transferring the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal to a muffle furnace for calcination to obtain a composite superstructured nanotube of In2O3-transition metal oxide-transition metal co-doped, wherein the second transition metal is doped within the In2O3 lattice, specifically includes: The In-MIL-68 crystal, co-doped with transition metal oxide and transition metal, is transferred to a muffle furnace, heated to a first preset temperature for initial calcination, and maintained for a first preset duration. The temperature is raised to a second preset temperature for final calcination and maintained for a second preset time to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, wherein the second transition metal is doped within the In2O3 lattice, and the second preset temperature is greater than the first preset temperature.

[0013] Specifically, the first preset temperature is any value within the range of 100℃ to 130℃; The second preset temperature is any value within the range of 300℃ to 550℃.

[0014] Specifically, in the step of transferring the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal into a muffle furnace, heating it to a first preset temperature for initial calcination, and continuing for a first preset time, air is introduced into the muffle furnace. In the step of heating to a second preset temperature for final calcination and continuing for a second preset time to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, oxygen is introduced into the muffle furnace.

[0015] Specifically, in the step of heating to a second preset temperature for final calcination and continuing for a second preset time to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, water vapor is added to the muffle furnace.

[0016] In the preparation of In-MIL-68 crystals, this invention adds a transition metal oxide precursor and a transition metal dopant to form In-MIL-68 crystals co-doped with transition metal oxides and transition metals. The In-MIL-68 crystals co-doped with transition metal oxides and transition metals are then calcined to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes. This invention uses the MOF template method to prepare the In2O3-transition metal oxide interface nanotube framework structure, constructing a heterogeneous interface synergistic system. Simultaneously, by introducing transition metal ion doping, oxygen vacancies and interface electronic states can be controlled, enhancing carbon dioxide activation.

[0017] Furthermore, the inventors of this invention discovered through research that directly heating the temperature to around 500°C during calcination causes the carbon in the MOF structure to disappear too quickly, making the structure prone to collapse and resulting in instability. Therefore, in calcining the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, this invention first performs initial calcination at a first preset temperature, essentially a pre-calcination, which helps stabilize the structure and increases the probability of obtaining the superstructure. Then, the temperature is raised to a second preset temperature for final calcination, where high-temperature calcination induces core decomposition and superstructure formation.

[0018] The above and other objects, advantages and features of the present invention will become more apparent to those skilled in the art from the following detailed description of specific embodiments of the invention in conjunction with the accompanying drawings. Attached Figure Description

[0019] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1This is a schematic flowchart of a method for preparing an indium oxide-based nanoparticle superstructure catalyst according to an embodiment of the present invention; Figure 2 This is an XRD pattern of an In2O3-ZrO2 composite structure according to an embodiment of the present invention; Figure 3 The XRD patterns of single-structure In2O3, In2O3-ZrO2 composite structure and In2O3-ZrO2-Fe composite superstructure nanotubes according to an embodiment of the present invention are shown. Figure 4 This is a schematic flowchart of a method for preparing an indium oxide-based nanoparticle superstructure catalyst according to another embodiment of the present invention; Figure 5 This is a TEM image of an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube according to an embodiment of the present invention. Figure 6 This is a magnified TEM image of an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube according to an embodiment of the present invention. Figure 7 The following are hydrogen temperature-programmed reduction diagrams for Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1; Figure 8 These are the EIS spectra of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1; Figure 9 The curves showing the relationship between methanol formation rate and time in the thermocatalytic stability test of Comparative Examples 1, 2, 3 and 1 within 13 hours are shown. Figure 10 These are TEM images of Example 1 at different scales; Figure 11 The image shows the EDS energy distributions of Ni, O, and In elements in Example 1. Figure 12 This is a schematic diagram of the methanol formation rate in the thermocatalytic CO2 hydrogenation to methanol test of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1; Figure 13 This is a particle size distribution chart of the In2O3-ZrO2-Ni co-doped nanoparticle unit in Example 1; Figure 14 This is a TEM image of Example 4; Figure 15 This is a HADDF-TEM image of Example 4; Figure 16 This is the EDS spectrum of Example 4; Figure 17 This is a TEM image of Example 5; Figure 18 This is a HADDF-TEM image of Example 5; Figure 19 This is the EDS spectrum of Example 5. Detailed Implementation

[0020] Figure 1 This is a schematic flowchart illustrating a method for preparing an indium oxide-based nanoparticle superstructure catalyst according to an embodiment of the present invention. Figure 1 As shown, in a specific embodiment, the preparation method of the indium oxide-based nanoparticle superstructure catalyst includes the following steps: Step S100: Dissolve In(NO3)3·xH2O and terephthalic acid in N,N-dimethylformamide to obtain a first mixed solution. The concentration of In(NO3)3 in the first mixed solution is any value between 0.8 mg / ml and 1.7 mg / ml, and the concentration of terephthalic acid is any value between 0.8 mg / ml and 1.7 mg / ml. In step S200, a transition metal oxide precursor and a transition metal dopant are added to the first mixed solution and stirred until dissolved to obtain a second mixed solution. The concentration of the transition metal oxide precursor in the second mixed solution is any value between 0.35 mg / ml and 0.8 mg / ml, and the concentration of the transition metal dopant is any value between 0.03 mg / ml and 0.25 mg / ml. The first transition metal in the transition metal oxide precursor is different from the second transition metal in the transition metal dopant. Step S300: The second mixed solution is transferred to a reaction vessel and heated to 120℃-150℃ for 12h-24h to obtain In-MIL-68 crystals co-doped with transition metal oxides and transition metals. In step S400, the In-MIL-68 crystal co-doped with transition metal oxide and transition metal is transferred to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doped, wherein the second transition metal is doped in the In2O3 lattice.

[0021] In this embodiment, during the preparation of In-MIL-68 crystals, a transition metal oxide precursor and a transition metal dopant are added to form an In-MIL-68 crystal co-doped with transition metal oxide and transition metal. Then, the In-MIL-68 crystal co-doped with transition metal oxide and transition metal is calcined to obtain an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube. This invention uses the MOF template method to prepare the In2O3-transition metal oxide interface nanotube framework structure and constructs a heterogeneous interface synergistic system. At the same time, by introducing transition metal ion doping, oxygen vacancies and interface electronic states can be controlled to enhance carbon dioxide activation.

[0022] Before establishing the method of constructing a synergistic interface structure between In₂O₃ and ZrO₂ / CeO₂, and further introducing a second transition metal dopant (such as Fe, Ni, Pb, or Sn) to regulate oxygen vacancies and adjust the interface electronic structure, thereby systematically improving the catalytic activity and selectivity of CO₂, the inventors attempted to introduce a single oxide component (such as ZrO₂ or CeO₂) as an interface regulating factor only during the pyrolysis of the MOF template. Their aim was to enhance the adsorption and activation of CO₂ molecules by leveraging its oxygen storage capacity and surface acidity / basicity. Although improvements in CO₂ adsorption capacity and a decrease in the low-temperature catalytic initiation point were observed in some samples, indicating that the synergistic oxide interface can improve catalytic performance to some extent, further research revealed that a single synergistic oxide is difficult to provide a sustained and stable electronic compensation, and the limited oxygen vacancy concentration and surface active sites result in limited improvement in reaction activity.

[0023] In addition, the inventors also attempted to induce a higher concentration of oxygen vacancies on the In2O3 surface by adjusting the calcination atmosphere, heat treatment procedure, or MOF ligand structure, and to optimize the pore structure to improve diffusion transport efficiency. However, these methods are effective in the initial stage of the reaction, but under high temperature or long-term reaction conditions, the interfacial structure is prone to reconstruction, resulting in a significant decline in catalytic performance, making it difficult to balance stability and structural uniformity.

[0024] Furthermore, the inventors attempted to introduce second transition metal doping (such as Fe, Ni, Pb, or Sn) as a means of electronic structure modulation in order to enhance the adsorption and polarization capabilities of CO2 molecules on the surface. However, when the dopant concentration is high or there is no interface synergistic structure to assist, it often leads to severe crystal phase distortion and excessive accumulation of defects, which in turn triggers side reaction pathways or carrier recombination, thereby limiting the reaction selectivity.

[0025] After failing to achieve a comprehensive performance improvement in multiple experiments, the inventors realized that relying solely on single-element regulation or interface modification was insufficient to meet the demands for synergistic optimization of activity, selectivity, and stability. Through further research, the inventors observed that by simultaneously pre-embedding Zr / Ce precursors into a MOF template to construct a synergistic interface structure, and introducing appropriate amounts of Fe, Ni, Pb, or Sn dopants, the resulting catalyst exhibited significant synergistic improvements in structural stability, oxygen vacancy concentration, charge distribution, and interfacial electron migration capabilities.

[0026] Through systematic verification, the inventors finally established the core technical solution of the present invention: namely, to prepare an In2O3-ZrO2 / CeO2 interface nanotube framework structure by using the MOF template method, to construct a heterogeneous interface synergistic system, and at the same time to introduce transition metal ions such as Fe, Ni, Pb or Sn for doping, so as to precisely control the oxygen vacancy concentration and the electronic state of the interface, thereby achieving systematic optimization of the CO2 activation path, electron transport behavior and intermediate control capabilities.

[0027] In step S100, the concentration of In(NO3)3 can be 0.8 mg / ml, 0.9 mg / ml, 1 mg / ml, 1.2 mg / ml, 1.3 mg / ml, 1.4 mg / ml, 1.5 mg / ml, 1.6 mg / ml, or 1.7 mg / ml. The concentration of terephthalic acid can be 0.8 mg / ml, 0.9 mg / ml, 1 mg / ml, 1.2 mg / ml, 1.3 mg / ml, 1.4 mg / ml, 1.5 mg / ml, 1.6 mg / ml, or 1.7 mg / ml.

[0028] In step S200, the concentration of the transition metal oxide precursor can be 0.35 mg / ml, 0.4 mg / ml, 0.45 mg / ml, 0.5 mg / ml, 0.6 mg / ml, 0.65 mg / ml, 0.7 mg / ml, 0.75 mg / ml, or 0.8 mg / ml. The concentration of the transition metal dopant can be 0.03 mg / ml, 0.06 mg / ml, 0.09 mg / ml, 0.12 mg / ml, 0.15 mg / ml, 0.18 mg / ml, 0.2 mg / ml, 0.22 mg / ml, or 0.25 mg / ml.

[0029] In step S300, the heating temperature can be 120℃, 125℃, 130℃, 135℃, 140℃, 145℃ or 150℃, and the duration can be 12h, 16h, 20h, 22h or 24h.

[0030] In step 300, after cooling to room temperature, the product is first diluted with ethanol and centrifuged at 11,000 rpm for 10 min to initially separate the solid product. Then, it is dispersed and washed three times with ethanol to obtain In-MIL-68 crystals co-doped with transition metal oxides and transition metals. Finally, it is naturally dried at room temperature for 24 h.

[0031] In some embodiments, the transition metal oxide precursor is ZrOCl2·8H2O, and the transition metal dopant is one of Fe(NO3)3·9H2O, Ni(NO)3·6H2O, Pb(NO3)2, and Sn(NO3)4. The In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is an In-MIL-68 crystal co-doped with ZrO2 and a second transition metal. For example, when Fe(NO3)3·9H2O is selected as the transition metal dopant, the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is an In-MIL-68 crystal co-doped with ZrO2 and Fe. When Ni(NO)3·6H2O is selected as the transition metal dopant, the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is an In-MIL-68 crystal co-doped with ZrO2 and Ni.

[0032] In some embodiments, the transition metal oxide precursor is Ce(NO3)3·6H2O, and the transition metal dopant is one of Fe(NO3)3·9H2O, Ni(NO)3·6H2O, Pb(NO3)2, and Sn(NO3)4. The In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is an In-MIL-68 crystal co-doped with CeO2 and a second transition metal. For example, when Fe(NO3)3·9H2O is selected as the transition metal dopant, the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is an In-MIL-68 crystal co-doped with CeO2 and Fe. When Ni(NO)3·6H2O is selected as the transition metal dopant, the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is an In-MIL-68 crystal co-doped with CeO2 and Ni.

[0033] This can be understood as the first transition metal being Zr or Ce, and the second transition metal being Fe, Ni, Pb, or Sn.

[0034] This embodiment uses In-MIL-68 as a template to prepare In2O3 nanotubes through pyrolysis. Simultaneously, Zr / Ce precursors are pre-embedded in the MOF to form an oxide-synergistic interface structure, such as In2O3-ZrO2 or In2O3-CeO2. By introducing the oxide-synergistic interface, more active activation centers are provided for CO2, enhancing its adsorption and activation capabilities. Furthermore, ZrO2 / CeO2 can act as a separator or carrier for In2O3 particles, limiting their aggregation at high temperatures. The stability of the oxide-synergistic interface structure is significantly better than that of the single-structure In2O3. Moreover, In2O3-ZrO2 or In2O3-CeO2 readily generates interfacial oxygen vacancies during calcination. These oxygen vacancies are key sites for CO2 activation, enabling stable adsorption of CO2 molecules and promoting the breaking of C=O bonds.

[0035] Fe in this embodiment 3+ The radius is smaller than In 3+ radius, Fe 3+ Entering the In₂O₃ lattice induces lattice strain, promoting the generation of oxygen vacancies, which is beneficial for the adsorption and activation of CO₂ molecules. Furthermore, the Fe-O-In sites formed after Fe doping have a synergistic promoting effect on CO₂ activation and hydrogen dissociation. In addition, Fe doping can modulate the band structure of In₂O₃, enhancing the interfacial electron density, which facilitates electron migration between surface active sites and improves the catalytic rate.

[0036] This embodiment adds a transition metal dopant, superimposing a new regulatory dimension on the basis of the transition metal oxide precursor, forming a dual synergistic mechanism to promote the formation and stability of oxygen vacancies. The stress field and electron rearrangement formed at the interface will induce more stable oxygen vacancies, increase the CO2 activation channel density, and enhance the dissociation ability of CO2.

[0037] Figure 2 This is an XRD pattern of an In2O3-ZrO2 composite structure according to an embodiment of the present invention, such as... Figure 2 As shown, the typical diffraction peak combination characteristics of In2O3 and ZrO2 are displayed. The characteristic peaks of In2O3 are approximately 30.6°, 35.5° and 51.1°, and the characteristic peaks of ZrO2 are approximately 28.2°, 31.5° and 50.3°. The multiple sets of peaks overlap or are close to each other, which shows their composite structure characteristics.

[0038] Figure 3 The XRD patterns of single-structure In2O3, In2O3-ZrO2 composite structure and In2O3-ZrO2-Fe composite superstructure nanotubes according to an embodiment of the present invention are shown below. Figure 3 As shown, the In₂O₃ single structure exhibits distinct and sharp diffraction peaks, typical of the In₂O₃ crystal structure. The peak positions correspond to the standard JCPDS card, with no peak broadening or shift. The In₂O₃-ZrO₂ composite structure, in addition to the main In₂O₃ peak, shows characteristic ZrO₂ peaks (e.g., 28.2°), with slightly wider peak widths, indicating the presence of grain boundaries or interactions. The main peak position of the In₂O₃-ZrO₂-Fe composite superstructure nanotube shifts slightly to the left and shows peak broadening, reflecting lattice distortion and coexistence with ZrO₂ interactions, demonstrating a combined synergistic structure and doping-induced dual-regulation characteristics.

[0039] Figure 4 This is a schematic flowchart illustrating a method for preparing an indium oxide-based nanoparticle superstructure catalyst according to another embodiment of the present invention. Figure 4 As shown, in another embodiment, the following steps are included after step S400: Step S500: Immerse the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes in a mixed solution of transition metal dopant and a polar organic solvent that is miscible with water and has coordination ability, and stir for 1-3 hours. Step S600: The hollow In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes after soaking are dried and then calcined again to obtain the doped In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes.

[0040] In step S500, the polar organic solvent that is miscible with water and has coordination ability can be ethanol, methanol, or DMF, etc.

[0041] In some embodiments, the following steps are included after step S400: Plasma reduction or UV-assisted reduction treatment was performed on In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes.

[0042] In this embodiment, when predoping is insufficient, post-processing can be used to enhance the stable embedding of dopant elements, improve their activity, and promote their entry into their lattice positions.

[0043] In step S600, the drying temperature is 60℃, the calcination temperature is 300℃, and the calcination time is 2h.

[0044] See Figure 4 In some embodiments, step S400 specifically includes: Step S410: Transfer the In-MIL-68 crystal co-doped with transition metal oxide and transition metal to a muffle furnace, heat it to a first preset temperature for initial calcination, and continue for a first preset time. In step S420, the temperature is raised to the second preset temperature for final calcination and maintained for the second preset time to obtain a composite superstructure nanotube co-doped with In2O3-transition metal oxide-transition metal, wherein the second transition metal is doped in the In2O3 lattice and the second preset temperature is greater than the first preset temperature.

[0045] In this invention, when calcining In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, an initial calcination is first performed at a first preset temperature, which is equivalent to pre-calcination. This helps to stabilize the structure and increases the probability of obtaining the superstructure. Then, the temperature is raised to a second preset temperature for final calcination. High-temperature calcination induces core decomposition and superstructure generation.

[0046] In some embodiments, the first preset temperature is any value in the range of 100°C to 130°C, for example, 100°C, 110°C, 120°C, or 130°C. The second preset temperature is any value in the range of 300°C to 550°C, for example, 300°C, 400°C, 450°C, 500°C, or 550°C.

[0047] In some embodiments, the first preset duration is any value between 2 and 3 hours, for example, 2 hours, 2.5 hours, or 3 hours. The second preset duration is any value between 2 and 3 hours, for example, 2 hours, 2.5 hours, or 3 hours.

[0048] In step S410, air is introduced into the muffle furnace. Under air atmosphere, the furnace is heated to 120°C at a heating rate of 5°C / min and held at that temperature for 2 hours. The main function of this stage is to slowly remove some functional groups from the organic ligands, suppress sudden structural collapse, and facilitate the formation of a dense outer shell while preserving the original tubular morphology of the MOF.

[0049] In step S420, oxygen is introduced into the muffle furnace. After low-temperature calcination, the furnace is heated to 500°C at a heating rate of 5°C / min under an oxygen atmosphere and held at that temperature for 2 hours to completely decompose the remaining organic ligands and simultaneously induce In... 3+ Ions are oxidized to crystalline In2O3. During this stage, the core pyrolysis rate is higher than the outer diffusion rate. The core material is gradually depleted, forming a void structure, and finally generating a composite superstructure nanotube with high specific surface area and abundant active sites, consisting of In2O3-transition metal oxide-transition metal co-doped nanotubes.

[0050] The In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes in this embodiment are hexagonal prisms, possessing good resistance to reduction and high carrier transport efficiency. Under a reducing atmosphere, they can generate a sufficient number of active sites to promote the reaction.

[0051] In some embodiments, in step S420, steam is added to the muffle furnace. The introduction of steam can induce hollowing.

[0052] Figure 5 This is a TEM image of an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube according to an embodiment of the present invention. Figure 6 This is a magnified TEM image of an In₂O₃-transition metal oxide-transition metal co-doped composite superstructure nanotube according to an embodiment of the present invention, such as... Figure 5 As shown, In-MIL-68 crystals co-doped with transition metal oxides and transition metals are calcined to form In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes. Figure 6TEM images show that particles are preferentially enriched at the edges and adjacent crystal faces.

[0053] Example 1: In(NO3)3·xH2O and terephthalic acid were dissolved in N,N-dimethylformamide to obtain a first mixed solution with an In(NO3)3 concentration of 1.2 mg / ml and a terephthalic acid concentration of 1.3 mg / ml. Then, ZrOCl2·8H2O and Ni(NO)3·6H2O were added to the first mixed solution and stirred until dissolved to obtain a second mixed solution with a ZrOCl2·8H2O concentration of 0.6 mg / ml and a Ni(NO)3·6H2O concentration of 0.1 mg / ml. The second mixed solution was then transferred to a reaction vessel and heated to 130°C for 18 hours to obtain ZrO2 and Ni co-doped In-MIL-68 crystals. Finally, the ZrO2 and Ni co-doped In-MIL-68 crystals were transferred to a muffle furnace for initial calcination at 120°C for 2 hours, followed by final calcination at 450°C for 2 hours, yielding In2O3-ZrO2-Ni co-doped composite superstructured nanotubes, with Ni doped within the In2O3 lattice. Air was introduced during the initial calcination, while oxygen and water vapor were introduced during the final calcination.

[0054] After obtaining the In2O3-ZrO2-Ni co-doped composite superstructured nanotubes, the In2O3-ZrO2-Ni co-doped composite superstructured nanotubes were immersed in a mixed solution of Ni(NO)3·6H2O and ethanol for 2 hours. Then, the immersed In2O3-ZrO2-Ni co-doped composite superstructured nanotubes were dried and calcined again to obtain the doped In2O3-ZrO2-Ni co-doped composite superstructured nanotubes.

[0055] Example 2: The only difference between Example 2 and Example 1 is that: The concentration of In(NO3)3 in the first mixed solution is 1.5 mg / ml, and the concentration of terephthalic acid is 1.2 mg / ml. The concentration of ZrOCl2·8H2O in the second mixed solution is 0.5 mg / ml, and the concentration of Ni(NO)3·6H2O is 0.15 mg / ml.

[0056] Example 3: The only difference between Example 3 and Example 1 is that: The concentration of In(NO3)3 in the first mixed solution is 0.9 mg / ml, and the concentration of terephthalic acid is 1 mg / ml. The concentration of ZrOCl2·8H2O in the second mixed solution is 0.7 mg / ml, and the concentration of Ni(NO)3·6H2O is 0.22 mg / ml.

[0057] Example 4: The only difference between Example 4 and Example 1 is that: Ni(NO)3·6H2O was replaced with Pb(NO3)2, and the concentration of Pb(NO3)2 was 0.12 mg / ml.

[0058] Example 5: The only difference between Example 5 and Example 1 is that: Ni(NO)3·6H2O was replaced with Sn(NO3)4, and the concentration of Sn(NO3)4 was 0.18 mg / ml.

[0059] Example 6: The only difference from Example 1 is: The ZrO2 and Ni co-doped In-MIL-68 crystals were transferred to a muffle furnace for calcination, directly heated to 450℃ and held for 2 hours to obtain In2O3-ZrO2-Ni co-doped composite superstructure nanotubes.

[0060] Comparative Example 1: The only difference from Example 1 is that ZrOCl2·8H2O and Ni(NO)3·6H2O are not added, and it is not necessary to soak in a mixed solution of Ni(NO)3·6H2O and ethanol, that is, no post-treatment is required.

[0061] Comparative Example 2: The only difference from Example 1 is that only ZrOCl2·8H2O is added, Ni(NO)3·6H2O is not added, and it is not necessary to soak in a mixed solution of Ni(NO)3·6H2O and ethanol, that is, no post-treatment is required.

[0062] Comparative Example 3: The only difference from Example 1 is that ZrOCl2·8H2O is not added, but only Ni(NO)3·6H2O is added.

[0063] Figure 7 This is a hydrogen temperature-programmed reduction diagram for Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1. (See diagram for reference.) Figure 7 As shown, the bulk In2O3 of Example 1 has the highest reduction temperature, confirming its resistance to reduction.

[0064] Figure 8These are the EIS spectra of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1. For example... Figure 8 As shown, Example 1 exhibited the smallest impedance radius in EIS testing, revealing a significant optimization of carrier mobility.

[0065] Figure 9 The curves show the relationship between methanol generation rate and time in the 13-hour thermocatalytic stability test of Comparative Examples 1, 2, 3 and 1. The unit of methanol generation rate refers to the molar mass of methanol catalyzed by a unit mass of catalyst per unit time. Figure 9 The thermocatalytic stability of Comparative Examples 1, 2, 3 and 1 in the CO2 hydrogenation to methanol reaction was tested over 13 hours. Example 1 maintained a methanol production rate of 92% at the peak when it finally stabilized, showing the best thermocatalytic stability.

[0066] Figure 10 These are TEM images of Example 1 at different scales, where... Figure 10 a and Figure 10 Image b is a TEM image of Example 1 at the 2-micrometer scale. Figure 10 c is a TEM image of Example 1 at the 1-micrometer scale. Figure 10 In the image, d is a TEM image of Example 1 at the 100nm scale. Figure 10 Image e is a 100nm local magnified TEM image from Example 1. From... Figure 10 a, Figure 10 b and Figure 10 As can be seen in Figure c, the addition of ZrO2-Ni to the system significantly shortened the length of the nanotubes. From... Figure 10 d and Figure 10 A complete hexagon can be observed in the sample, and this hexagon is surrounded by In2O3-ZrO2-Ni particles, which further confirms the existence of the superstructure.

[0067] Figure 11 These are the EDS spectra of Ni, O, and In elements in Example 1. The left image shows the EDS spectrum of Ni, the middle image shows the EDS spectrum of O, and the right image shows the EDS spectrum of In, demonstrating the uniform distribution of Ni, O, and In elements on the nanotube.

[0068] Figure 12This is a schematic diagram illustrating the methanol formation rate in the thermocatalytic CO2 hydrogenation to methanol test of Comparative Examples 1, 2, 3, and 1. Comparative Example 1 is a hollow In2O3 nanotube prepared without the addition of ZrOCl2·8H2O and Ni(NO)3·6H2O; Comparative Example 2 is a hollow In2O3-ZrO2 nanotube prepared with the addition of ZrOCl2·8H2O but without the addition of Ni(NO)3·6H2O; and Comparative Example 3 is a hollow In2O3-Ni nanotube prepared without the addition of ZrOCl2·8H2O but with the addition of Ni(NO)3·6H2O. Examples 1, 2, and 3 are In2O3-ZrO2-Ni composite superstructured nanotubes prepared by simultaneously adding ZrOCl2·8H2O and Ni(NO)3·6H2O. In the thermocatalytic test of CO2 hydrogenation to methanol, we found that the In2O3-ZrO2-Ni composite superstructured nanotubes significantly improved the methanol formation rate at 250℃-280℃ (the optimal reaction range for CO2 hydrogenation to methanol), confirming that the incorporation of ZrO2-Ni accelerates electron migration at the interface, promotes the adsorption of reaction intermediates, and thus promotes the CO2 hydrogenation to methanol reaction.

[0069] Figure 13 This is a particle size distribution chart of the In2O3-ZrO2-Ni co-doped nanoparticle unit in Example 1. Figure 13 It was confirmed that the tube wall was composed of oriented assembly of In2O3-ZrO2-Ni co-doped composite grains with an average particle size of approximately 8 nm, forming a regular hollow topology. In Example 6, without an initial calcination stage, the temperature was directly raised to 450°C for calcination. The resulting In2O3-ZrO2-Ni co-doped composite grains had an average particle size greater than 8 nm, approximately 15 nm. This indicates that initial calcination can effectively control grain growth, avoiding excessively large grains during direct high-temperature calcination, and reducing structural instability caused by thermal stress.

[0070] Figure 14 This is a TEM image of Example 4. Figure 15 This is a HADDF-TEM image from Example 4. Figure 16 This is the EDS spectrum of Example 4. Figure 17 This is a TEM image of Example 5. Figure 18 This is a HADDF-TEM image from Example 5. Figure 19 This is the EDS spectrum of Example 5. From Figures 14 to 19 The morphology shows that different transition metal doping can slightly change the shape of the nanotubes, but the overall structure still maintains the superstructure.

[0071] Therefore, those skilled in the art should recognize that although numerous exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications conforming to the principles of the present invention can be directly determined or derived from the disclosure of the present invention without departing from the spirit and scope of the invention. Thus, the scope of the present invention should be understood and construed as covering all such other variations or modifications.

Claims

1. A method for preparing an indium oxide-based nanoparticle superstructure catalyst, characterized in that: The following steps are involved: Dissolving In(NO3)3·xH2O and terephthalic acid in N,N-dimethylformamide to obtain a first mixed solution, wherein the concentration of In(NO3)3 in the first mixed solution is any value between 0.8 mg / ml and 1.7 mg / ml, and the concentration of terephthalic acid is any value between 0.8 mg / ml and 1.7 mg / ml; Adding a transition metal oxide precursor and a transition metal dopant to the first mixed solution, stirring evenly until dissolved, to obtain a second mixed solution, wherein the concentration of the transition metal oxide precursor in the second mixed solution is any value between 0.35 mg / ml and 0.8 mg / ml, the concentration of the transition metal dopant is any value between 0.03 mg / ml and 0.25 mg / ml, and the first transition metal in the transition metal oxide precursor is different from the second transition metal in the transition metal dopant; The second mixed solution is transferred to a reaction kettle, heated to 120° C.-150° C., and continued for 12 h-24 h to obtain In-MIL-68 crystals co-doped with transition metal oxide and transition metal; The transition metal oxide and transition metal co-doped In-MIL-68 crystals are transferred to a muffle furnace for calcination to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, wherein the second transition metal is doped in the In2O3 lattice.

2. The preparation method according to claim 1, characterized in that: The transition metal oxide precursor is ZrOCl2·8H2O, and the transition metal dopant is one of Fe(NO3)3·9H2O, Ni(NO)3·6H2O, Pb(NO3)2 and Sn(NO3)4; The transition metal oxide and transition metal co-doped In-MIL-68 crystal is ZrO2 and the second transition metal co-doped In-MIL-68 crystal.

3. The preparation method according to claim 1, characterized in that: The transition metal oxide precursor is Ce(NO3)3·6H2O, and the transition metal dopant is one of Fe(NO3)3·9H2O, Ni(NO)3·6H2O, Pb(NO3)2 and Sn(NO3)4; The transition metal oxide and transition metal co-doped In-MIL-68 crystal is CeO2 and the second transition metal co-doped In-MIL-68 crystal.

4. The preparation method according to claim 1, characterized in that: The transition metal oxide and the transition metal co-doped In-MIL-68 crystal are transferred to a muffle furnace for calcination to obtain an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, wherein the second transition metal is doped in the In2O3 lattice, and then the following steps are further included: Immersing the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube in a mixed solution of the transition metal dopant and a polar organic solvent that is polar, miscible with water and has coordination ability, and stirring for 1 h to 3 h; The In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube after immersion is dried and calcined again to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube after doping treatment.

5. The preparation method according to claim 1, characterized in that: The transition metal oxide and the transition metal co-doped In-MIL-68 crystal are transferred to a muffle furnace for calcination to obtain an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, wherein the second transition metal is doped in the In2O3 lattice, and then the following steps are further included: The In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube is subjected to plasma reduction treatment or ultraviolet-assisted reduction treatment.

6. The preparation method according to claim 1, characterized in that: The transition metal oxide and the transition metal co-doped In-MIL-68 crystal are transferred to a muffle furnace for calcination to obtain an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, wherein the second transition metal is doped in the In2O3 lattice, specifically comprising: Transferring the transition metal oxide and the transition metal co-doped In-MIL-68 crystal to a muffle furnace, heating to a first preset temperature for initial calcination, and continuing for a first preset time; The temperature is raised to a second preset temperature for final calcination, and continued for a second preset time to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, wherein the second transition metal is doped in the In2O3 lattice, and the second preset temperature is greater than the first preset temperature.

7. The preparation method according to claim 6, characterized in that: The first preset temperature is any value in the range of 100°C to 130°C; The second preset temperature is any value in the range of 300° C. to 550° C.

8. The preparation method according to claim 6, characterized in that: In the step of transferring the transition metal oxide and the transition metal co-doped In-MIL-68 crystal into a muffle furnace, heating to a first preset temperature for initial calcination, and continuing the calcination for a first preset time, air is introduced into the muffle furnace; In the step of heating to a second preset temperature for final calcination and continuing for a second preset time to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, oxygen is introduced into the muffle furnace.

9. The preparation method according to claim 8, characterized in that: In the step of heating to a second preset temperature for final calcination and continuing for a second preset time to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, water vapor is added to the muffle furnace.

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