An iridium single-atom / iridium nanocluster composite catalyst, its preparation method and application

Abstract

This invention belongs to the field of hydrogen energy materials technology, specifically relating to an iridium single-atom / iridium nanocluster composite catalyst, its preparation method, and its application. The preparation method includes the following steps: dissolving an organic ligand, a zirconium salt, and an iridium source in an organic solvent, and obtaining a metal-organic framework anchored to iridium ions through a solvothermal reaction; calcining the obtained metal-organic framework anchored to iridium ions at high temperature to obtain the iridium single-atom / nanocluster composite catalyst. The obtained composite catalyst has a high specific surface area, good catalytic activity, and catalytic site selectivity, and can efficiently catalyze the selective hydrogenation of 3-nitrostyrene to nitro (selectivity > 50%), with a TOF value > 650 h⁻¹. ‑1 It exhibits catalytic activity far exceeding that of commercial iridium catalysts and possesses excellent cycle stability, making it a promising candidate for large-scale selective hydrogenation reactions.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen energy materials technology. More specifically, it relates to an iridium single-atom / iridium nanocluster composite catalyst, its preparation method, and its application. Background Technology

[0002] In nature, organic compounds commonly contain unsaturated sites, a characteristic that necessitates precise processing to produce high-purity chemical products. Therefore, the chemical community pays particular attention to the selective hydrogenation of aromatic compounds with multiple unsaturated sites. This is especially true for compounds with small differences in unsaturated bond energies, such as nitrostyrene, which contains both nitro and carbon-carbon double bonds. The N=O bond energy is 607 kJ / mol, while the C=C bond energy is 615 kJ / mol. The energy required for complete hydrogenation to NO2 is far higher than that for hydrogenation to C=C, making highly selective hydrogenation of the nitro group even more difficult. However, the nitro hydrogenation product of nitrostyrene—aminostyrene—can be used in the chemical industry to manufacture high-value-added chemicals, such as dyes, pigments, pharmaceuticals, and agrochemicals.

[0003] In the selective hydrogenation of nitrostyrene, traditional techniques often employ commercial catalysts combined with solid hydrogen evolution agents (such as NaBH4 and LiAlH4). However, these solid hydrogen evolution agents are not only expensive but also generate large amounts of waste liquid that require treatment after the reaction, placing a burden on the environment. Therefore, in recent years, researchers have begun to turn to using highly active nanocatalysts combined with hydrogen for catalytic hydrogenation, aiming to reduce costs and minimize environmental impact.

[0004] While the combination of nanocatalysts and hydrogen has potential advantages, the active hydrogen generated during hydrogen activation differs in properties from that released by solid hydrogen evolution agents. Hydrogen activation is typically achieved through heterolytic cleavage, and the resulting active hydrogen may carry either a positive or negative charge. This causes them to favor carbon-carbon double bonds with lower hydrogen bond energies rather than nitro groups. Therefore, in the selective hydrogenation of nitrostyrene, using hydrogen as the hydrogen source often faces the problem of low selectivity for 3-aminostyrene.

[0005] Furthermore, currently available commercially available precious metal catalysts do not perform satisfactorily in the selective catalytic hydrogenation of nitrostyrene, failing to efficiently generate high-value-added products. Although some selective hydrogenation nitro catalysts have been developed, they still have shortcomings in terms of selectivity or reaction rate. For example, while some cobalt single-atom catalysts (CN109939718A) can effectively catalyze nitro hydrogenation under certain conditions, their catalytic activity remains low, with a TOF value of less than 400 h⁻¹. -1 This limits their potential in industrial applications.

[0006] In summary, there is an urgent need to develop a novel catalyst that possesses both high selectivity and high reactivity to efficiently and efficiently obtain the selective hydrogenation products of nitro groups. Summary of the Invention

[0007] The technical problem to be solved by this invention is to overcome the many challenges still faced by the existing selective hydrogenation technology of nitrostyrene, including the high cost of solid hydrogen evolution agents, the difficulty of waste liquid treatment, the poor selectivity of active hydrogen generated by hydrogen activation, and the low catalytic activity of existing catalysts. This invention provides a method for preparing an iridium single atom / nanocluster composite catalyst.

[0008] The purpose of this invention is to provide an iridium single-atom / nanocluster composite catalyst prepared by the aforementioned method.

[0009] Another object of the present invention is to provide the application of the iridium single-atom / nanocluster composite catalyst.

[0010] The above-mentioned objective of this invention is achieved through the following technical solution:

[0011] This invention protects a method for preparing an iridium single-atom / nanocluster composite catalyst, comprising the following steps:

[0012] S1. The amino-containing organic ligand, zirconium salt and iridium source are fully dissolved in an organic solvent and subjected to a solvothermal reaction at 80-200℃. After post-treatment, a metal-organic framework anchored to iridium ions is obtained.

[0013] S2. Under an inert protective atmosphere, the metal-organic framework anchored with iridium ions obtained in step S1 is fully calcined at 500–1000 °C to obtain an iridium single-atom / nanocluster composite catalyst.

[0014] This invention employs a simple solvothermal method to obtain an Ir ion-anchored MOF precursor. Subsequent simple high-temperature calcination yields an iridium single-atom / nanocluster composite catalyst. This catalyst exhibits high specific surface area, excellent catalytic activity, and catalytic site selectivity, enabling highly efficient catalysis of the selective hydrogenation of 3-nitrostyrene (selectivity > 50%), with a TOF value > 650 h⁻¹. -1 It exhibits catalytic activity far exceeding that of commercial iridium catalysts and demonstrates excellent stability during recycling.

[0015] Preferably, the amino-containing organic ligand includes one or more of 2-aminobenzoic acid, 2-aminoterephthalic acid, and 2,5-diaminoterephthalic acid. The metal-organic framework mainly consists of organic ligands and coordinating metal sites. The special -NH2 group on the organic ligand can enhance the adsorption capacity for non-coordinating metals. Subsequently, a simple soaking-washing process is sufficient to anchor individual metal ions, and calcination yields single-atom sites.

[0016] More preferably, the amino-containing organic ligand is 2-aminobenzoic acid.

[0017] Preferably, the zirconium salt includes zirconium tetrachloride, zirconium sulfate, zirconium citrate, or a hydrate of any of the above zirconium salts.

[0018] More preferably, the zirconium salt is zirconium tetrachloride.

[0019] Preferably, the iridium source includes iridium chloride, chloroiridic acid, sodium chloroiridate, or a hydrate of any of the above iridium salts.

[0020] More preferably, the iridium salt is hydrated iridium chloride.

[0021] Preferably, the organic solvent includes one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, and acetonitrile.

[0022] Further, the molar ratio of the zirconium salt, the amino-containing organic ligand, and the iridium source is (0.2-7):(0.2-7):1, more preferably (0.5-5):(0.5-5):1, and even more preferably (4-5):(4-5):1.

[0023] Furthermore, the mass-to-volume ratio of the zirconium salt to the organic solvent is 1:(1-8) mg / mL, more preferably 1:(2-5) mg / mL.

[0024] Preferably, the solvothermal heating rate is 2–10 °C / min.

[0025] Preferably, the solvothermal reaction temperature is 120–150°C.

[0026] Preferably, the solvothermal reaction time is 8 to 48 hours, more preferably 10 to 30 hours.

[0027] Preferably, the calcination temperature is 600–900°C, more preferably 650–750°C. The catalyst prepared using the method of this application can have its catalytic activity and catalytic site selectivity optimized by further adjusting the calcination temperature. The reaction rate far exceeds that of commercial catalysts, while maintaining a 3-aminostyrene selectivity of over 50%. Furthermore, it can be recycled multiple times without catalytic performance degradation, demonstrating great application potential.

[0028] Preferably, the heating rate for the complete calcination is 2 to 10 °C / min.

[0029] Furthermore, the calcination time is 1 to 5 hours.

[0030] Furthermore, the calcination temperature is 600–900°C, and the calcination time is 2–3 hours.

[0031] Furthermore, the inert protective atmosphere is provided by a protective gas selected from nitrogen, argon, or helium, preferably argon.

[0032] Furthermore, the complete dissolution is achieved by using ultrasound and stirring to promote dissolution.

[0033] Furthermore, the post-processing includes cooling, centrifugation, washing, and drying.

[0034] Furthermore, the cooling is natural cooling.

[0035] Furthermore, the centrifugation conditions are 5000-10000 rpm for 5-20 min.

[0036] Furthermore, the washing process involves washing with DMF 3 to 5 times, followed by washing with ethanol 1 to 3 times.

[0037] Furthermore, the drying is vacuum drying, and the vacuum drying conditions are 40-100℃ for 4-24 hours.

[0038] This invention also protects iridium single-atom / nanocluster composite catalysts prepared by any of the preparation methods described above.

[0039] Furthermore, the iridium single-atom / nanocluster composite catalyst comprises co-anchored iridium single atoms and iridium nanoclusters. Since the specific surface area of ​​the single atoms and nanoclusters is greater than that of conventional nanoparticles, the resulting composite catalyst exhibits a high specific surface area.

[0040] Furthermore, the iridium nanoclusters are sub-nanometer-sized particles composed of multiple iridium atoms.

[0041] Furthermore, the iridium loading in the iridium single-atom / nanocluster composite catalyst is 0.01wt% to 2wt%, preferably 0.03wt% to 0.7wt%, and more preferably 0.05wt% to 0.1wt%.

[0042] This invention also protects the application of the iridium single-atom / nanocluster composite catalyst in the selective hydrogenation reaction of unsaturated aromatic compounds.

[0043] Furthermore, the unsaturated aromatic compound includes compounds with any of the following structures:

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] This invention employs a simple solvothermal method to obtain an Ir ion-anchored MOF precursor. Subsequent high-temperature calcination is sufficient to obtain an iridium single-atom / nanocluster composite catalyst. The specific preparation method includes the following steps: dissolving an organic ligand, zirconium salt, and iridium source in an organic solvent, and obtaining an iridium ion-anchored metal-organic framework through a solvothermal reaction; calcining the obtained iridium ion-anchored metal-organic framework at high temperature to obtain the iridium single-atom / nanocluster composite catalyst. The resulting composite catalyst exhibits high specific surface area, good catalytic activity, and catalytic site selectivity, and can efficiently catalyze the selective hydrogenation of 3-nitrostyrene (selectivity > 50%), with a TOF value > 650 h⁻¹. -1 It exhibits catalytic activity far exceeding that of commercial iridium catalysts and possesses excellent cycle stability, making it a promising candidate for large-scale selective hydrogenation reactions. Attached Figure Description

[0046] Figure 1 The image shows the XRD powder diffraction pattern of the precursor IrCl3 / UiO-66-NH2 obtained in step S1 of Example 1.

[0047] Figure 2 The images show the XRD powder diffraction patterns of the four composite catalysts obtained in Examples 1-4.

[0048] Figure 3 The image shows a transmission electron microscope (TEM) image and elemental distribution diagram of the composite catalyst IrSA-ZrO2-700 obtained in Example 1.

[0049] Figure 4 This is a high-angle annular dark field diagram of the composite catalyst IrSA-ZrO2-700 obtained in Example 1.

[0050] Figure 5 The X-ray absorption spectra of the composite catalysts obtained in Examples 1-4 are shown.

[0051] Figure 6 A schematic diagram of selective hydrogenation of 3-nitrostyrene.

[0052] Figure 7 The figures show the performance of the catalyst IrSA-ZrO2-X (600, 700, 800, 900℃) obtained in Examples 1-4 (corresponding to figures a, b, c, and d) in the selective hydrogenation of 3-nitrostyrene.

[0053] Figure 8 The graph shows the performance of the composite catalyst IrSA-ZrO2-700 obtained in Example 1 after 5 cycles. Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0055] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0056] Figure 7 a represents Figure 7 Figure a in the middle, Figure 7 b represents Figure 7 The meanings of the other names in Figure b are similar.

[0057] The commercial catalyst Commercial Ir / C is sourced from Shanghai Jizhi Technology Co., Ltd., where the mass fraction of Ir in the Ir / C is 10%.

[0058] Example 1: A method for preparing an iridium single-atom / iridium nanocluster composite catalyst

[0059] 1.48 mg ZrCl4 was added to 120 mL of dimethylformamide (DMF), and sonicated for 5 minutes. Then, 37.2 mg 2-aminoterephthalic acid (NH2-BDC) was added, and the mixture was sonicated for another 5 minutes. Then, 150 μL of IrCl3·H2O containing 0.05 mmol was added, and the mixture was stirred vigorously for 30 minutes. The mixture was then transferred to a 150 mL hydrothermal reactor, sealed with a stainless steel shell, and heated from room temperature to 120 °C at a rate of 5 °C per minute in an oven at 120 °C for 24 hours. After the reactor cooled naturally, the mixture was transferred to centrifuge tubes and centrifuged at 8000 rpm for 5 minutes to obtain a yellow powder. This powder was then washed three times with DMF, once with ethanol, and dried under vacuum at 150 °C overnight to obtain the precursor IrCl3 / UiO-66-NH2.

[0060] S2. Disperse 100 mg of IrCl3 / UiO-66-NH2 obtained in step S1 evenly in a crucible, place it in the center of a tube furnace, introduce Ar, and heat from room temperature to 700°C at a rate of 5°C per minute, maintain for 2 hours, and wait for natural cooling. The resulting catalyst is named Ir SA-ZrO2-700.

[0061] Example 2: A method for preparing an iridium single-atom / iridium nanocluster composite catalyst

[0062] The difference from Example 1 is that the calcination temperature in step S2 is 600°C, while the other experimental conditions are the same as in Example 1. The resulting catalyst is named IrSA-ZrO2-600.

[0063] Example 3: A method for preparing an iridium single-atom / iridium nanocluster composite catalyst

[0064] The difference from Example 1 is that the calcination temperature in step S2 is 800°C, while the other experimental conditions are the same as in Example 1. The resulting catalyst is named IrSA-ZrO2-800.

[0065] Example 4: A method for preparing an iridium single-atom / iridium nanocluster composite catalyst

[0066] The difference from Example 1 is that the calcination temperature in step S2 is 900°C, while the other experimental conditions are the same as in Example 1. The resulting catalyst is named Ir SA-ZrO2-900.

[0067] Comparative Example 1: Preparation method of catalyst ZrO2-700

[0068] The difference from Example 1 is that IrCl3·H2O is not added in step S1, while other experimental conditions are the same as in Example 1, and the resulting catalyst is named ZrO2-700.

[0069] Experimental Example Performance Determination

[0070] (1) XRD determination

[0071] The precursor IrCl3 / UiO-66-NH2 obtained in step S1 was determined by XRD, and the results are as follows: Figure 1 As shown, the crystal form of the Ir ion-anchored precursor IrCl3 / UiO-66-NH2 is consistent with that of the original MOF UiO-66-NH2.

[0072] The composite catalysts obtained in Examples 1-4 were subjected to XRD analysis, and the results are as follows: Figure 2 As shown, the main component of the catalyst after high-temperature calcination is ZrO2, and no diffraction peaks of elemental Ir were found. With increasing calcination temperature, the diffraction peaks become sharper, indicating a higher degree of crystallinity of ZrO2.

[0073] (2) Determination of morphology and elemental distribution

[0074] The composite catalyst obtained in Example 1 was subjected to transmission electron microscopy and elemental distribution analysis. The results are as follows: Figure 3 As shown, based on the observed lattice fringes, the main component of the catalyst is ZrO2, and N, Ir, and Zr are uniformly distributed in the catalyst.

[0075] The composite catalyst obtained in Example 1 was analyzed using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and the results are as follows: Figure 4 As shown, many brighter spots can be found, which are Ir single atoms. The higher the atomic number, the brighter the atom.

[0076] (3) X-ray absorption spectroscopy measurement

[0077] The X-ray absorption spectra of the composite catalysts obtained in Examples 1-4 were measured, and the results are as follows: Figure 5 As shown, using Ir powder and IrO2 as standard samples, the specific bond lengths of Ir-Ir and Ir-O bonds can be determined. The figure shows that all four catalysts exhibit Ir-Ir and Ir-O bonds, indicating the coexistence of Ir nanoclusters and Ir single atoms. The Ir-Ir bond strength is highest at 900℃, suggesting that increasing the calcination temperature promotes the aggregation of Ir atoms into nanoclusters.

[0078] (4) ICP-MS test

[0079] 1. Experimental Methods

[0080] Weigh 5g of catalyst and add it to 10mL of aqua regia (a mixture of concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO3) in a volume ratio of 3:1), sonicate for 30 minutes, dilute with deionized water 1000 times, and test the Ir content using an instrument.

[0081] 2. Experimental Results

[0082] Table 1. IrC containing Ir precursors obtained in Examples 1-4 l3 Mass fraction of Ir in / UiO-66-NH2 and Ir SA-ZrO2-X (X=600,700,800,900)

[0083] Group Precursor / catalyst Ir loading / wt% precursor <![CDATA[IrC13 / UiO-66-NH2]]> 0.028 Example 2 <![CDATA[Ir SA-ZrO2-600]]> 0.059 Example 1 <![CDATA[Ir SA-ZrO2-700]]> 0.065 Example 3 <![CDATA[Ir SA-ZrO2-800]]> 0.056 Example 4 <![CDATA[IrSA-ZrO2-900]]> 0.061

[0084] The results are shown in Table 1. The Ir content of the catalyst obtained after calcination is approximately twice that of the precursor. This is because some carbon and oxygen components are lost during the calcination process, leading to an increase in the Ir content. The Ir content of the calcined catalysts is roughly the same, all below 0.1 wt%, indicating that the catalyst prepared by this method requires only trace amounts of precious metals, resulting in a low overall cost.

[0085] (5) Catalytic reaction testing methods

[0086] (5.1) Performance determination of selective hydrogenation at different catalytic reaction times

[0087] 1. Experimental Methods

[0088] In the inner liner of a high-pressure reactor, 5 mg of catalyst was dispersed in 3 mL of n-butanol, and 0.2 mmol of 3-nitrostyrene was added. The reactor was then assembled. Hydrogen gas was introduced to a pressure of 1 MPa and then released, repeated at least three times to remove as much air as possible. The reaction temperature was 90 °C, and the rotation speed was 600 rpm. After the reaction was completed, a small amount of the mixture was transferred to a centrifuge tube, centrifuged, and the supernatant was diluted with ethanol. The catalytic results were identified using gas chromatography-mass spectrometry (GC-MS).

[0089] 2. Experimental Results

[0090] Schematic diagram of selective hydrogenation of 3-nitrostyrene Figure 6 As shown, there are three products, including 3-aminostyrene (3-AS), 3-nitrobenzene (3-EN), and 3-aminoethylbenzene (3-EA).

[0091] The performance of the catalysts IrSA-ZrO2-X (600, 700, 800, 900) obtained in Examples 1-4 for the selective hydrogenation of 3-nitrostyrene is shown in the figure below. Figure 7 As shown in a to d, all four catalysts exhibit high selectivity in catalyzing the hydrogenation of nitro groups to produce 3-aminostyrene. Among them, [the catalysts used are from...] Figure 7 b shows that Ir SA-ZrO2-700 can catalyze the hydrogenation of nitro to produce 3-aminostyrene with high selectivity, and the substrate conversion rate can reach 99% in only 4 hours of reaction. The product selectivity and substrate conversion rate are both optimal.

[0092] (5.2) Performance determination of selective hydrogenation with fixed catalytic reaction time

[0093] 1. Experimental Methods

[0094] In a high-pressure reactor, disperse 5 mg of catalyst (or 0.5 mg Ir / C (where Ir content is 10 wt%)) in 3 mL of n-butanol, add 0.3 mmol of 3-nitrostyrene, and assemble the reactor. Purge with hydrogen to 1 MPa and then release, repeating this process at least three times to remove as much air as possible. The reaction temperature is 90 °C, the rotation speed is 600 rpm, and the reaction time is 6 h. After the reaction is complete, take a small amount of the mixture into a centrifuge tube, centrifuge, collect the supernatant, dilute with ethanol, and use GC-MS to identify the catalytic results.

[0095] 2. Experimental Results

[0096] Table 2 shows the performance and product selectivity results of the selective hydrogenation of 3-nitrostyrene in Examples 1-4, Comparative Example 1, and the commercial catalyst.

[0097]

[0098] The results are shown in Table 2. The selectivity of the catalysts Ir SA-ZrO2-X (600, 700, 800, 900) obtained in Examples 1 to 4 for 3-aminostyrene (3-AS) is greater than 50%. Among them, Ir SA-ZrO2-700 has the highest catalytic selectivity and catalytic activity, which is far superior to commercial catalysts. Its total activity per unit mass (TOF) is about 200 times that of commercial catalysts.

[0099] (5.3) Performance determination of selective hydrogenation of different substrates

[0100] 1. Experimental Methods

[0101] In the inner liner of a high-pressure reactor, 5 mg of IrSA-ZrO2-700 catalyst was dispersed in 3 mL of n-butanol, and 0.2 mmol of different substrates were added (as shown in Table 3). The reactor was then assembled. Hydrogen gas was introduced to a pressure of 1 MPa and then released, repeated at least three times to remove as much air as possible. The reaction temperature was 90 °C, the rotation speed was 600 rpm, and the reaction time was 4 h. After the reaction was completed, a small amount of the mixture was transferred to a centrifuge tube, centrifuged, and the supernatant was diluted with ethanol. The catalytic results were identified by GC-MS.

[0102] 2. Experimental Results

[0103] Table 3. Hydrogenation results of different nitrobenzene derivatives catalyzed by Ir SA-ZrO2-700

[0104]

[0105] Using the IrSA-ZrO2-700 obtained in Example 1 as a representative catalyst, it was used for the selective hydrogenation of unsaturated bonds in other nitrobenzene derivatives containing unsaturated groups. The results are shown in Table 3. This catalyst can efficiently catalyze the selective hydrogenation of unsaturated bonds in a variety of nitrobenzene derivatives containing unsaturated groups. The product selectivity and substrate conversion rate can both reach 99.9%, indicating that the catalyst has universality in catalytic hydrogenation.

[0106] (5.4) Determination of cycle performance

[0107] 1. Experimental Methods

[0108] In a high-pressure reactor, 5 mg of IrSA-ZrO2-700 was dispersed in 3 mL of n-butanol, and 0.3 mmol of 3-nitrostyrene was added. The reactor was then assembled. Hydrogen gas was introduced to a pressure of 1 MPa and then released, repeated at least three times to remove as much air as possible. The reaction temperature was 90℃, the rotation speed was 600 rpm, and the reaction time was 6 h. After the reaction was completed, a small amount of the mixture was transferred to a centrifuge tube, centrifuged, and the supernatant was collected. The supernatant was diluted with ethanol, and the catalytic results were identified by GC-MS. The remaining supernatant was removed with a pipette, ethanol was added, and the mixture was sonicated for 5 minutes to disperse the catalyst and dissolve the organic matter adsorbed on the catalyst. The mixture was then centrifuged again, and the supernatant was removed. This process was repeated at least three times. After the catalyst was allowed to air dry, the next cycle performance test was performed.

[0109] 2. Experimental Results

[0110] The results of recycling the catalyst IrSA-ZrO2-700 five times are as follows: Figure 8 As shown, the catalyst showed no decrease in catalytic selectivity and catalytic activity after five consecutive uses, indicating that it has excellent stability for repeated use.

[0111] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing an iridium single-atom / nanocluster composite catalyst, characterized in that, Includes the following steps: S1. The amino-containing organic ligand, zirconium salt and iridium source are fully dissolved in an organic solvent and subjected to a solvothermal reaction at 80-200℃. After post-treatment, a metal-organic framework anchored to iridium ions is obtained. S2. Under an inert protective atmosphere, the metal-organic framework anchored with iridium ions obtained in step S1 is fully calcined at 500–1000 °C to obtain an iridium single-atom / nanocluster composite catalyst.

2. The preparation method according to claim 1, characterized in that, The amino-containing organic ligands include one or more of 2-aminobenzoic acid, 2-aminoterephthalic acid, and 2,5-diaminoterephthalic acid.

3. The preparation method according to claim 1, characterized in that, The zirconium salt includes zirconium tetrachloride, zirconium sulfate, zirconium citrate, or a hydrate of any of the above zirconium salts.

4. The preparation method according to claim 1, characterized in that, The iridium source includes iridium chloride, chloroiridic acid, sodium chloroiridate, or a hydrate of any of the above iridium salts.

5. The preparation method according to claim 1, characterized in that, The organic solvent includes one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and acetonitrile.

6. The preparation method according to claim 1, characterized in that, The molar ratio of the zirconium salt, the amino-containing organic ligand, and the iridium source is (0.2–7):(0.2–7):

1.

7. The iridium single-atom / nanocluster composite catalyst prepared by any of the preparation methods described in claims 1 to 6.

8. The iridium single-atom / nanocluster composite catalyst according to claim 7, characterized in that, The iridium single-atom / nanocluster composite catalyst comprises co-anchored iridium single atoms and iridium nanoclusters.

9. The iridium single-atom / nanocluster composite catalyst according to claim 7, characterized in that, The iridium loading in the iridium single-atom / nanocluster composite catalyst is 0.01wt% to 2wt%.

10. The application of the iridium single-atom / nanocluster composite catalyst according to any one of claims 7 to 9 in the selective hydrogenation reaction of unsaturated aromatic compounds.

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