Preparation method of indium oxide-based nanoparticle superstructure catalyst

Abstract

The present invention provides a method for preparing an indium oxide-based nanoparticle superstructure catalyst, which relates to the technical field of catalyst preparation. During the preparation of In-MIL-68 crystals in the present invention, a transition metal oxide precursor and a transition metal dopant are added to form an In-MIL-68 crystal co-doped with a transition metal oxide and a transition metal. Then, the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal is calcined to obtain a composite superstructure nanotube co-doped with In2O3-transition metal oxide-transition metal. The present invention uses the MOF template method to prepare the In2O3-transition metal oxide interface nanotube framework structure, constructs a heterojunction interface synergistic system, and at the same time, by introducing transition metal ion doping, the oxygen vacancy and interface electron state can be regulated, the catalytic performance is improved, and the carbon dioxide activation is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and particularly to a method for preparing an indium oxide-based nanoparticle superstructure catalyst. Background Art

[0002] In the methanol synthesis reaction, although low-temperature conditions (<200 °C) help to suppress the reverse water-gas shift side reaction (RWGS), they also result in too low a kinetic rate; while high-temperature environments (>250 °C) can improve the reaction efficiency, but they exacerbate catalyst sintering deactivation and selectivity decline. Existing copper-based and palladium-based catalysts generally face bottlenecks such as poor anti-sintering properties and high precious metal dependence. Especially during continuous operation, migration of active components or structural collapse is likely to occur, making it difficult to meet the long-term stability requirements of industrial plants.

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

[0004] In the prior art, In(NO3)3·xH2O and terephthalic acid are usually dissolved in a DMF solvent to obtain In-MIL-68, and then transferred to a muffle furnace for calcination to obtain In2O3 nanotubes with a hollow tubular morphology. The catalytic activity of the obtained hollow tubular In2O3 nanotubes is not very good, so it is urgent to design In2O3 superstructure nanotubes with better catalytic activity. Summary of the Invention

[0005] An object of the present invention is to provide a method for preparing an indium oxide-based nanoparticle superstructure catalyst to solve the technical problem of poor catalytic activity of hollow tubular In2O3 nanotubes.

[0006] A further object of the present invention is to improve the thermal catalytic stability of the 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:

[0008] 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 in the range of 0.8 mg / ml to 1.7 mg / ml, and the concentration of terephthalic acid is any value in the range of 0.8 mg / ml to 1.7 mg / ml;

[0009] Add a transition metal oxide precursor and a transition metal dopant to the first mixed solution, stir 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 in the range of 0.35 mg / ml to 0.8 mg / ml, the concentration of the transition metal dopant is any value in the range of 0.03 mg / ml to 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;

[0010] Transfer the second mixed solution to a reaction kettle, heat it to 120 °C - 150 °C, and maintain for 12 h - 24 h to obtain In-MIL-68 crystals co-doped with a transition metal oxide and a transition metal;

[0011] Transfer the In-MIL-68 crystals co-doped with a transition metal oxide and a transition metal to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping, and the second transition metal is doped in the lattice of In2O3.

[0012] In particular, 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;

[0013] The In-MIL-68 crystals co-doped with a transition metal oxide and a transition metal are In-MIL-68 crystals co-doped with ZrO2 and the second transition metal.

[0014] In particular, 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;

[0015] The In-MIL-68 crystals co-doped with a transition metal oxide and a transition metal are In-MIL-68 crystals co-doped with CeO2 and the second transition metal.

[0016] Specifically, transfer the In-MIL-68 crystal co-doped with the transition metal oxide and transition metal to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping. The step of doping the second transition metal into the lattice of In2O3 is followed by the following steps:

[0017] Immerse the composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping in a mixed solution of the transition metal dopant and a polar organic solvent with polarity, water solubility, and coordination ability, and stir for 1 h - 3 h;

[0018] Dry the immersed composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping and perform re-calcination to obtain the composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping after doping treatment.

[0019] Specifically, transfer the In-MIL-68 crystal co-doped with the transition metal oxide and transition metal to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping. The step of doping the second transition metal into the lattice of In2O3 is followed by the following steps:

[0020] Perform plasma reduction treatment or ultraviolet-assisted reduction treatment on the composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping.

[0021] Specifically, the step of doping the second transition metal into the lattice of In2O3 by transferring the In-MIL-68 crystal co-doped with the transition metal oxide and transition metal to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping specifically includes:

[0022] Transfer the In-MIL-68 crystal co-doped with the transition metal oxide and transition metal to a muffle furnace, raise the temperature to a first preset temperature for initial calcination, and continue for a first preset duration;

[0023] Raise the temperature to a second preset temperature for final calcination, and continue for a second preset duration to obtain the composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping, wherein the second transition metal is doped into the lattice of In2O3, and the second preset temperature is higher than the first preset temperature.

[0024] Specifically, the first preset temperature is any value in the range of 100 °C to 130 °C;

[0025] The second preset temperature is any value within the range of 300°C to 550°C.

[0026] Particularly, in the step of transferring the transition metal oxide and transition metal co-doped In-MIL-68 crystal into a muffle furnace, heating it to the first preset temperature for initial calcination, and maintaining the first preset duration, air is introduced into the muffle furnace;

[0027] In the step of heating to the second preset temperature for final calcination and maintaining the second preset duration to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, oxygen is introduced into the muffle furnace.

[0028] Particularly, in the step of heating to the second preset temperature for final calcination and maintaining the second preset duration to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, water vapor is added into the muffle furnace.

[0029] In the process of preparing the In-MIL-68 crystal of the present invention, a transition metal oxide precursor and a transition metal dopant are added to form a 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 In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes. The present invention adopts the MOF template method to prepare the In2O3-transition metal oxide interface nanotube framework structure, constructs a heterojunction interface synergistic system, and at the same time, by introducing transition metal ion doping, the oxygen vacancies and interface electron states can be regulated to enhance carbon dioxide activation.

[0030] Furthermore, the inventor of the present invention found through research that when directly heating to about 500°C for calcination during calcination, the C in the MOF structure disappears too fast, the structure is prone to collapse, and an unstable situation occurs. Therefore, when calcining the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes of the present invention, initial calcination is first carried out at the first preset temperature, which is equivalent to pre-calcination first, helping to stabilize the structure and the probability of obtaining the superstructure is better, and then heating to the second preset temperature for final calcination, and high-temperature calcination induces the decomposition of the inner core and the formation of the superstructure.

[0031] From the following detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will more clearly understand the above and other objects, advantages and features of the present invention. Description of the Drawings

[0032] Some specific embodiments of the present invention will be described in detail hereinafter with reference to the accompanying drawings in an exemplary but not limiting manner. The same reference numerals in the drawings denote the same or similar components or parts. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings:

[0033] Figure 1 is a schematic flow chart of a preparation method of an indium oxide-based nanoparticle superstructure catalyst according to an embodiment of the present invention;

[0034] Figure 2 is an XRD pattern of an In2O3-ZrO2 composite structure according to an embodiment of the present invention;

[0035] Figure 3 is an XRD pattern of a single structure In2O3, an In2O3-ZrO2 composite structure, and a composite superstructure nanotube of In2O3-ZrO2-Fe according to an embodiment of the present invention;

[0036] Figure 4 is a schematic flow chart of a preparation method of an indium oxide-based nanoparticle superstructure catalyst according to another embodiment of the present invention;

[0037] Figure 5 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;

[0038] Figure 6 is a local enlarged TEM image of an In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube according to an embodiment of the present invention;

[0039] Figure 7 is a hydrogen temperature-programmed reduction graph of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1;

[0040] Figure 8 is an EIS spectrum of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1;

[0041] Figure 9 is a relationship curve of the methanol production rate and time in the thermal catalytic stability test of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1 for 13 h;

[0042] Figure 10 is a TEM image of Example 1 at different scales;

[0043] Figure 11 is an EDS energy spectrum diagram of Ni element, O element, and In element in Example 1;

[0044] Figure 12Schematic diagram of the methanol production rate in the thermal catalytic CO2 hydrogenation to methanol tests of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1;

[0045] Figure 13 Statistical chart of the particle size of the In2O3-ZrO2-Ni co-doped nanoparticle unit in Example 1;

[0046] Figure 14 TEM image of Example 4;

[0047] Figure 15 HADDF-TEM image of Example 4;

[0048] Figure 16 EDS energy spectrum of Example 4;

[0049] Figure 17 TEM image of Example 5;

[0050] Figure 18 HADDF-TEM image of Example 5;

[0051] Figure 19 EDS energy spectrum of Example 5. Detailed implementation manners

[0052] Figure 1 Schematic flow chart of a method for preparing an indium oxide-based nanoparticle superstructure catalyst according to an embodiment of the present invention. As Figure 1 shown, in a specific embodiment, the method for preparing an indium oxide-based nanoparticle superstructure catalyst includes the following steps:

[0053] Step S100, 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 in the range of 0.8 mg / ml - 1.7 mg / ml, and the concentration of terephthalic acid is any value in the range of 0.8 mg / ml - 1.7 mg / ml;

[0054] Step S200, adding a transition metal oxide precursor and a transition metal dopant to the first mixed solution, and 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 in the range of 0.35 mg / ml - 0.8 mg / ml, the concentration of the transition metal dopant is any value in the range of 0.03 mg / ml - 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;

[0055] Step S300: Transfer the second mixed solution into a reaction kettle, heat it to 120°C - 150°C, and keep it for 12 h - 24 h to obtain In-MIL-68 crystals co-doped with transition metal oxides and transition metals;

[0056] Step S400: Transfer the In-MIL-68 crystals co-doped with transition metal oxides and transition metals into a muffle furnace for calcination to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, and the second transition metal is doped into the lattice of In2O3.

[0057] In the process of preparing In-MIL-68 crystals in this example, a transition metal oxide precursor and a transition metal dopant are added to form In-MIL-68 crystals co-doped with transition metal oxides and transition metals, and then the In-MIL-68 crystals co-doped with transition metal oxides and transition metals are calcined to obtain In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes. The present invention uses the MOF template method to prepare the In2O3-transition metal oxide interface nanotube framework structure, constructs a heterojunction interface synergy system, and at the same time, by introducing transition metal ion doping, the oxygen vacancies and interface electron states can be regulated to enhance the activation of carbon dioxide.

[0058] Before establishing the realization of oxygen vacancy regulation and interface electron structure regulation by constructing the In2O3 and ZrO2 / CeO2 synergy interface structure and further introducing a second transition metal doping element (such as Fe, Ni, Pb, or Sn) to systematically improve the CO2 catalytic activity and selectivity, the inventors attempted to introduce a single oxide component (such as ZrO2 or CeO2) as an interface regulation factor only during the MOF template pyrolysis process, aiming to enhance the adsorption and activation of CO2 molecules by virtue of its oxygen storage capacity and surface acidity and basicity. Although an improvement in the CO2 adsorption capacity and a decrease in the low-temperature catalytic starting point were observed in some samples, indicating that the synergy oxide interface can improve the catalytic performance to a certain extent. However, further research found that a single synergy oxide is difficult to continuously and stably provide electron compensation, and at the same time, the oxygen vacancy concentration and surface active sites are limited, resulting in limited improvement in the reaction activity.

[0059] In addition, the inventors also attempted to induce the formation of a higher concentration of oxygen vacancies on the surface of In2O3 by adjusting the calcination atmosphere, heat treatment procedure, or MOF ligand structure, and optimize the pore structure to improve the diffusion and transport efficiency. However, these means are effective in the initial stage of the reaction, but under high-temperature or long-time reaction conditions, the interface structure is prone to reconstruction, resulting in obvious decline in catalytic performance and it is difficult to balance stability and structural uniformity.

[0060] Furthermore, the inventors attempted to introduce a second transition metal doping (such as Fe, Ni, Pb, or Sn) as a means of electronic structure regulation, with the expectation of enhancing the adsorption and polarization ability of CO2 molecules on the surface. However, when the dopant concentration is relatively high or there is no interfacial cooperative structure to assist, it often leads to severe crystal phase distortion and excessive aggregation of defects, which instead triggers side reaction pathways or carrier recombination, thereby limiting the reaction selectivity.

[0061] Against the backdrop of multiple experiments failing to achieve a systematic improvement in performance, the inventors found that relying solely on single-element regulation or interfacial modification methods was no longer sufficient to meet the requirements of synergistically optimizing activity, selectivity, and stability. Through further research, the inventors observed that after simultaneously pre-embedding Zr / Ce element precursors in the MOF template to construct a cooperative interfacial structure and introducing an appropriate amount of Fe, Ni, Pb, or Sn dopants, the resulting catalyst showed a significant synergistic improvement in terms of structural stability, oxygen vacancy concentration, charge distribution, and interfacial electron migration ability.

[0062] After systematic verification, the inventors finally established the core technical solution of the present invention: namely, using the MOF template method to prepare an In2O3-ZrO2 / CeO2 interfacial nanotube framework structure, constructing a heterogeneous interfacial cooperative system, and at the same time introducing transition metal ion doping such as Fe, Ni, Pb, or Sn to precisely regulate the oxygen vacancy concentration and interfacial electron state, so as to systematically optimize the CO2 activation path, electron transport behavior, and intermediate regulation ability.

[0063] 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.

[0064] 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.

[0065] In step S300, the heating temperature can be 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C or 150 °C, and the duration can be 12 h, 16 h, 20 h, 22 h or 24 h.

[0066] In step 300, after cooling to room temperature, first dilute with ethanol, centrifuge at 11000 rpm for 10 min to initially separate out the solid product, and then disperse and wash with ethanol three times to obtain the In-MIL-68 crystal co-doped with transition metal oxide and transition metal. Finally, air-dry at room temperature for 24 h.

[0067] 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 transition metal oxide and transition metal is the In-MIL-68 crystal co-doped with ZrO2 and a second transition metal. For example, when the transition metal dopant is Fe(NO3)3·9H2O, the In-MIL-68 crystal co-doped with transition metal oxide and transition metal is the In-MIL-68 crystal co-doped with ZrO2 and Fe. When the transition metal dopant is Ni(NO)3·6H2O, the In-MIL-68 crystal co-doped with transition metal oxide and transition metal is the In-MIL-68 crystal co-doped with ZrO2 and Ni.

[0068] 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 transition metal oxide and transition metal is the In-MIL-68 crystal co-doped with CeO2 and a second transition metal. For example, when the transition metal dopant is Fe(NO3)3·9H2O, the In-MIL-68 crystal co-doped with transition metal oxide and transition metal is the In-MIL-68 crystal co-doped with CeO2 and Fe. When the transition metal dopant is Ni(NO)3·6H2O, the In-MIL-68 crystal co-doped with transition metal oxide and transition metal is the In-MIL-68 crystal co-doped with CeO2 and Ni.

[0069] It can be understood that the first transition metal can be Zr or Ce, and the second transition metal can be Fe, Ni, Pb or Sn.

[0070] In this example, In-MIL-68 was used as a template to prepare In2O3 nanotubes by pyrolysis. At the same time, Zr / Ce element precursors were 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 were provided for CO2, enhancing the CO2 adsorption and activation ability. In addition, ZrO2 / CeO2 can act as a separator or carrier for In2O3 particles, restricting 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 is prone to generate interfacial oxygen vacancies during the calcination process, and oxygen vacancies are the key sites for CO2 activation, which can stably adsorb CO2 molecules and promote the cleavage of the C=O bond.

[0071] In this example, Fe 3+ has a smaller radius than In 3+ . When Fe 3+ enters the In2O3 lattice, it will cause lattice strain, promote the generation of oxygen vacancies, and is beneficial to the adsorption and activation of CO2 molecules. Moreover, the Fe-O-In sites formed after Fe doping have a synergistic promoting effect on the activation of CO2 and the dissociation of hydrogen. In addition, after Fe doping, the band structure of In2O3 can be adjusted, enhancing the interfacial electron density, which helps the migration of electrons between surface active sites and improves the catalytic rate.

[0072] In this example, transition metal dopants were added, adding a new regulation dimension on the basis of transition metal oxide precursors to form a dual synergistic mechanism, promoting the formation and stability of oxygen vacancies. The stress field and electron rearrangement formed at the interface will induce more stable oxygen vacancies, increasing the CO2 activation channel density and enhancing the CO2 dissociation ability.

[0073] Figure 2 is the XRD pattern of the In2O3-ZrO2 composite structure according to an embodiment of the present invention, as Figure 2 shown, showing the typical diffraction peak combination characteristics of In2O3 and ZrO2. 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°. Multiple groups of peaks overlap or are close, showing the characteristics of its composite structure.

[0074] Figure 3 is the XRD pattern of the single structure In2O3, In2O3-ZrO2 composite structure, and In2O3-ZrO2-Fe composite superstructure nanotubes according to an embodiment of the present invention, as Figure 3As shown, the In2O3 single structure has obvious and sharp diffraction peaks, which are typical of the In2O3 crystal structure. The peak positions correspond to the standard JCPDS cards, and there is no peak broadening or shift. Based on the main peak of In2O3, the In2O3-ZrO2 composite structure shows characteristic peaks of ZrO2 (such as 28.2°), and the peak width is slightly larger, indicating the existence of a certain degree of grain boundaries or interactions. The main peak position of the In2O3-ZrO2-Fe composite superstructure nanotubes shifts slightly to the left, and peak broadening occurs, reflecting lattice distortion and coexistence of interactions with ZrO2, showing the characteristics of dual regulation of the composite synergistic structure + doping.

[0075] Figure 4 is a schematic flowchart of a method for preparing an indium oxide-based nanoparticle superstructure catalyst according to another embodiment of the present invention. As Figure 4 shown, in another embodiment, after step S400, the following steps are further included:

[0076] Step S500, soaking the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes in a mixed solution of a transition metal dopant and a polar organic solvent that is polar, water-miscible, and has coordination ability, and stirring for 1 h - 3 h;

[0077] Step S600, drying the soaked hollow In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes and performing calcination again to obtain the doped In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes.

[0078] In step S500, the polar organic solvent that is polar, water-miscible, and has coordination ability can be ethanol, methanol, DMF, etc.

[0079] In some embodiments, after step S400, the following steps are further included:

[0080] Performing plasma reduction treatment or ultraviolet-assisted reduction treatment on the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes.

[0081] In this embodiment, when the pre-doping is insufficient, the stable embedding of the doping elements can be enhanced by post-treatment, the activity of the doping elements can be improved, and their entry into their lattice positions can be promoted.

[0082] In step S600, the drying temperature is 60 °C, the calcination temperature is 300 °C, and the calcination duration is 2 h.

[0083] See Figure 4 , in some embodiments, step S400 specifically includes:

[0084] Step S410: Transfer the In-MIL-68 crystal co-doped with transition metal oxide and transition metal into a muffle furnace, heat it up to the first preset temperature for initial calcination, and maintain the temperature for the first preset duration.

[0085] Step S420: Heat it up to the second preset temperature for final calcination, and maintain the temperature for the second preset duration to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes. The second transition metal is doped in the lattice of In2O3, and the second preset temperature is higher than the first preset temperature.

[0086] When the present invention calcines the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes, it first performs initial calcination at the first preset temperature, which is equivalent to pre-calcination first, helping to stabilize the structure and increasing the probability of obtaining the superstructure. Then, it is heated up to the second preset temperature for final calcination, and high-temperature calcination induces the decomposition of the inner core and the formation of the superstructure.

[0087] In some embodiments, the first preset temperature is any value within the range of 100°C to 130°C, such as 100°C, 110°C, 120°C, or 130°C. The second preset temperature is any value within the range of 300°C to 550°C, such as 300°C, 400°C, 450°C, 500°C, or 550°C.

[0088] In some embodiments, the first preset duration is any value within the range of 2 - 3 h, such as 2 h, 2.5 h, or 3 h. The second preset duration is any value within the range of 2 - 3 h, such as 2 h, 2.5 h, or 3 h.

[0089] In step S410, introduce air into the muffle furnace. Under an air atmosphere, heat it at a heating rate of 5°C / min to 120°C and maintain the temperature for 2 hours. The main function of this stage is to slowly remove some functional groups in the organic ligands, inhibit the sudden collapse of the structure, and is conducive to forming a dense outer shell layer and retaining the original tubular morphology of the MOF.

[0090] In step S420, introduce oxygen into the muffle furnace. After the low-temperature calcination is completed, under an oxygen atmosphere, heat it at a heating rate of 5°C / min to 500°C and maintain the temperature for 2 hours to completely decompose the remaining organic ligands, and at the same time induce the oxidation of In 3+ ions to crystalline In2O3. In this stage, the pyrolysis rate of the inner core is higher than the outer diffusion rate, and the inner core material is gradually depleted, forming a hollow structure, and finally generating the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes with a high specific surface area and abundant active sites.

[0091] The In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes of this embodiment are hexagonal prism-shaped, have good anti-reduction properties and high carrier transport efficiency, and can generate a sufficient number of active sites in a reducing atmosphere to promote the reaction.

[0092] In some embodiments, in step S420, water vapor is added to the muffle furnace. The introduction of water vapor can induce hollowing.

[0093] Figure 5 is a TEM image of In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes according to an embodiment of the present invention, Figure 6 is a local enlarged TEM image of In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes according to an embodiment of the present invention, as Figure 5 shown, the In-MIL-68 crystal co-doped with transition metal oxide and transition metal forms In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotubes after calcination. Figure 6 The TEM image of shows that the particles are preferentially enriched in the edge and adjacent crystal plane regions.

[0094] Example 1:

[0095] 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 1.2 mg / ml, and the concentration of terephthalic acid is 1.3 mg / ml. Then add ZrOCl2·8H2O and Ni(NO)3·6H2O to the first mixed solution and stir evenly until dissolved to obtain a second mixed solution. The concentration of ZrOCl2·8H2O in the second mixed solution is 0.6 mg / ml, and the concentration of Ni(NO)3·6H2O is 0.1 mg / ml. Then transfer the second mixed solution to a reaction kettle, heat it to 130 °C, and keep it for 18 h to obtain In-MIL-68 crystals co-doped with ZrO2 and Ni. Finally, transfer the In-MIL-68 crystals co-doped with ZrO2 and Ni to a muffle furnace for initial calcination, heat it to 120 °C, and keep it for 2 h, then heat it to 450 °C for final calcination and keep it for 2 h to obtain In2O3-ZrO2-Ni co-doped composite superstructure nanotubes, and Ni is doped in the lattice of In2O3. Air is introduced during the initial calcination process, and oxygen and water vapor are introduced during the final calcination process.

[0096] After obtaining the In2O3-ZrO2-Ni co-doped composite superstructure nanotubes, the In2O3-ZrO2-Ni co-doped composite superstructure nanotubes are immersed in a mixed solution of Ni(NO)3·6H2O and ethanol, stirred for 2 h, and then the immersed In2O3-ZrO2-Ni co-doped composite superstructure nanotubes are dried and calcined again to obtain the doped In2O3-ZrO2-Ni co-doped composite superstructure nanotubes.

[0097] Example 2:

[0098] The difference between Example 2 and Example 1 is only that:

[0099] 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.

[0100] Example 3:

[0101] The difference between Example 3 and Example 1 is only that:

[0102] 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.

[0103] Example 4:

[0104] The difference between Example 4 and Example 1 is only that:

[0105] Ni(NO)3·6H2O is replaced by Pb(NO3)2, and the concentration of Pb(NO3)2 is 0.12 mg / ml.

[0106] Example 5:

[0107] The difference between Example 5 and Example 1 is only that:

[0108] Ni(NO)3·6H2O is replaced by Sn(NO3)4, and the concentration of Sn(NO3)4 is 0.18 mg / ml.

[0109] Example 6:

[0110] The difference from Example 1 is only that:

[0111] Transfer the ZrO2 and Ni co-doped In-MIL-68 crystals to a muffle furnace for calcination. Heat it directly to 450 °C and keep it for 2 h to obtain the In2O3-ZrO2-Ni co-doped composite superstructure nanotubes.

[0112] Comparative Example 1:

[0113] The difference from Example 1 is only that ZrOCl2·8H2O and Ni(NO)3·6H2O are not added, and there is no need to soak in the mixed solution of Ni(NO)3·6H2O and ethanol, that is, no post-treatment is required.

[0114] Comparative Example 2:

[0115] The difference from Example 1 is only that only ZrOCl2·8H2O is added, Ni(NO)3·6H2O is not added, and there is no need to soak in the mixed solution of Ni(NO)3·6H2O and ethanol, that is, no post-treatment is required.

[0116] Comparative Example 3:

[0117] The difference from Example 1 is only that ZrOCl2·8H2O is not added, and only Ni(NO)3·6H2O is added.

[0118] Figure 7 It is the temperature-programmed reduction of hydrogen for Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1. As Figure 7 shown, the reduction temperature of the bulk In2O3 in Example 1 is the highest, verifying its anti-reduction property.

[0119] Figure 8 It is the EIS spectra of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1. As Figure 8 shown, Example 1 shows the smallest impedance radius in the EIS test, revealing a significant optimization of the carrier mobility.

[0120] Figure 9 It is the relationship curve between the methanol production rate and time in the 13 h thermal catalytic stability test of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1. The unit of the methanol production rate refers to the molar mass of methanol catalytically produced by the catalyst per unit mass per unit time. Figure 9 It shows the thermal catalytic stability test of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 in the reaction of hydrogenating CO2 to methanol within 13 h. Example 1 can still maintain a methanol production rate equivalent to 92% of the highest point at the end of stability, showing the best thermal catalytic stability.

[0121] Figure 10 It is the TEM image of Example 1 at different scales. Among them, Figure 10 in a andFigure 10 In Figure b is the TEM image of Example 1 at a scale of 2 μm, Figure 10 In Figure c is the TEM image of Example 1 at a scale of 1 μm, Figure 10 In Figure d is the TEM image of Example 1 at a scale of 100 nm, Figure 10 In Figure e is the 100 nm local enlarged TEM image of Example 1. From Figure 10 In Figure a, Figure 10 In Figure b, and Figure 10 In Figure c, it can be seen that the addition of the ZrO2-Ni system significantly shortens the length of the nanotubes. From Figure 10 In Figure d and Figure 10 In Figure e, a complete hexagon can be observed, and this hexagon is surrounded by In2O3-ZrO2-Ni small particles, further confirming the existence of the superstructure.

[0122] Figure 11 is the EDS spectrum of Ni element, O element and In element in Example 1. Among them, the left figure is the EDS spectrum of Ni element, the middle figure is the EDS spectrum of O element, and the right figure is the EDS spectrum of In element, showing the uniform distribution of Ni element, O element and In element on the nanotubes.

[0123] Figure 12 is a schematic diagram of the methanol production rate in the thermal catalytic CO2 hydrogenation to methanol tests of Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1. Among them, Comparative Example 1 is the hollow In2O3 nanotubes prepared without adding ZrOCl2·8H2O and Ni(NO)3·6H2O, Comparative Example 2 is the hollow In2O3-ZrO2 nanotubes prepared by adding ZrOCl2·8H2O and without adding Ni(NO)3·6H2O, and Comparative Example 3 is the hollow In2O3-Ni nanotubes prepared without adding ZrOCl2·8H2O but adding Ni(NO)3·6H2O. Examples 1, 2 and 3 are the composite superstructure nanotubes of In2O3-ZrO2-Ni prepared by adding ZrOCl2·8H2O and Ni(NO)3·6H2O at the same time. In the thermal catalytic test of CO2 hydrogenation to methanol, we found that the composite superstructure nanotubes of In2O3-ZrO2-Ni significantly increased the methanol production rate at 250 °C - 280 °C (the most suitable reaction range for CO2 hydrogenation to methanol), confirming that the incorporation of ZrO2-Ni accelerated the electron migration at the interface, promoted the adsorption of reaction intermediates and thus promoted the CO2 hydrogenation to methanol reaction.

[0124] Figure 13 is the particle size statistical chart of the In2O3-ZrO2-Ni co-doped nanoparticle unit in Example 1. Figure 13It is confirmed that the tube wall is composed of the directional assembly of composite grains co-doped with In2O3-ZrO2-Ni with an average particle size of about 8 nm, forming a regular hollow topology. In Example 6, without going through the initial calcination stage, it was directly heated to 450 °C for calcination. The average particle size of the co-doped composite grains of In2O3-ZrO2-Ni made would be greater than 8 nm, about 15 nm. This shows that the initial calcination can effectively control the growth of grains, avoid excessive grain size during direct high-temperature calcination, and reduce the structural instability caused by thermal stress.

[0125] Figure 14 is the TEM image of Example 4, Figure 15 is the HADDF-TEM image of Example 4, Figure 16 is the EDS spectrum of Example 4, Figure 17 is the TEM image of Example 5, Figure 18 is the HADDF-TEM image of Example 5, Figure 19 is the EDS spectrum of Example 5. From Figures 14 to 19 the morphology, it can be found that after doping with different transition metals, the shape of the nanotubes can be slightly changed, but the overall superstructure is still maintained.

[0126] Up to this point, those skilled in the art should recognize that although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived from the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and determined to cover all these other variations or modifications.

Claims

1. A method for preparing an indium oxide-based nanoparticle superstructure catalyst, characterized in that, It includes 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 in the range of 0.8 mg / ml - 1.7 mg / ml, and the concentration of terephthalic acid is any value in the range of 0.8 mg / ml - 1.7 mg / ml; Add a transition metal oxide precursor and a transition metal dopant to the first mixed solution, stir 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 in the range of 0.35 mg / ml - 0.8 mg / ml, the concentration of the transition metal dopant is any value in the range of 0.03 mg / ml - 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; Transfer the second mixed solution to a reaction kettle, heat it to 120°C - 150°C and keep it for 12 h - 24 h to obtain In-MIL-68 crystals co-doped with a transition metal oxide and a transition metal; Transfer the In-MIL-68 crystals co-doped with a transition metal oxide and a transition metal to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping, and the second transition metal is doped in the lattice of In2O3; After the step of transferring the In-MIL-68 crystals co-doped with a transition metal oxide and a transition metal to a muffle furnace for calcination to obtain a composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping, and the second transition metal is doped in the lattice of In2O3, the following steps are further included: Immerse the composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping in a mixed solution of the transition metal dopant and a polar organic solvent with polarity, water solubility and coordination ability, and stir for 1 h - 3 h; Dry the immersed composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping and perform re-calcination to obtain the doped composite superstructure nanotube of In2O3-transition metal oxide-transition metal co-doping.

2. The preparation method according to claim 1, wherein 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 crystals co-doped with a transition metal oxide and a transition metal are In-MIL-68 crystals co-doped with ZrO2 and the second transition metal.

3. The preparation method according to claim 1, wherein 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 the In-MIL-68 crystal co-doped with CeO2 and the second transition metal.

4. The preparation method according to claim 1, wherein After 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 the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, where the second transition metal is doped in the lattice of In2O3, the following steps are further included: Performing plasma reduction treatment or ultraviolet-assisted reduction treatment on the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube.

5. The preparation method according to claim 1, characterized in that, 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 the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, where the second transition metal is doped in the lattice of In2O3, specifically includes: Transferring the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal to a muffle furnace, heating to a first preset temperature for initial calcination, and maintaining for a first preset duration; Heating to a second preset temperature for final calcination, and maintaining for a second preset duration to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, where the second transition metal is doped in the lattice of In2O3, and the second preset temperature is higher than the first preset temperature.

6. The preparation method according to claim 5, 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.

7. The preparation method according to claim 5, characterized in that In the step of transferring the In-MIL-68 crystal co-doped with the transition metal oxide and the transition metal to a muffle furnace, heating to a first preset temperature for initial calcination, and maintaining for a first preset duration, air is introduced into the muffle furnace; In the step of heating to a second preset temperature for final calcination, and maintaining for a second preset duration to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, oxygen is introduced into the muffle furnace.

8. The preparation method according to claim 7, characterized in that In the step of heating to a second preset temperature for final calcination, and maintaining for a second preset duration to obtain the In2O3-transition metal oxide-transition metal co-doped composite superstructure nanotube, water vapor is added to the muffle furnace.

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