A composite catalyst and its preparation method, a photoelectrocatalytic system, and a method for preparing organic carbonates by photoelectrocatalytic reduction of carbon dioxide.

Abstract

This invention relates to the fields of photoelectrocatalytic materials and carbon dioxide resource utilization, and discloses a composite catalyst and its preparation method, a photoelectrocatalytic system, and a method for preparing organic carbonates by photoelectrocatalytic reduction of carbon dioxide. The composite catalyst is formed by combining silver-doped titanium dioxide particles with hydroxylated carbon nanotubes; the structural formula of the composite catalyst is Ag1 / TiO2-(OH)CNTs. The composite catalyst provided by this invention can directly and selectively convert CO2 into organic carbonates, and exhibits good stability and substrate scalability; it provides a new strategy for the performance innovation of traditional semiconductors and the high-value utilization of CO2.

Description

Technical Field

[0001] This invention relates to the field of photoelectrocatalytic materials and carbon dioxide resource utilization technology, specifically to a composite catalyst and its preparation method, a photoelectrocatalytic system, and a method for preparing organic carbonates by photoelectrocatalytic reduction of carbon dioxide. Background Technology

[0002] Titanium dioxide (TiO2) has been widely studied in the field of photocatalysis due to its advantages such as non-toxicity, low cost, and good stability. However, the wide bandgap of TiO2 (approximately 3.2 eV) limits its absorption of visible light, photogenerated electron-hole pairs recombine rapidly, and its adsorption and activation capabilities for CO2 molecules are relatively weak. These inherent defects mean that traditional TiO2-based catalysts typically only produce C1 products (such as CO and HCOOH) in the photoelectrocatalytic CO2 reduction reaction, making it difficult to achieve highly selective synthesis of multi-carbon products (such as dimethyl carbonate and diethyl carbonate).

[0003] Currently, the main modification strategies for TiO2 include metal or non-metal doping, nanostructure manipulation, and heterostructure construction. However, these methods mostly focus on improving light absorption or charge separation, making it difficult to simultaneously achieve efficient CO2 activation, intermediate stabilization, and synergistic catalysis of multi-step reactions. While single-atom catalysts can provide highly active sites, their stable loading on wide-bandgap semiconductors and efficient coupling with photogenerated carriers still face challenges.

[0004] For example, in the field of TiO2-based photocatalytic CO2 reduction, although existing technologies have explored various aspects, none have simultaneously solved the four core problems of electronic structure regulation, charge lifetime, CO2 activation efficiency, and intermediate stability. Specifically, some technologies have improved charge separation through heterojunction interface engineering (e.g., CN114011467A), but have not paid enough attention to CO2 activation and intermediate stability; some technologies have introduced piezoelectric effects to significantly extend charge lifetime (e.g., CN118109849A), but have no application to CO2 reduction; some technologies have achieved visible light response and high selectivity for C1 products through defect regulation (e.g., CN107827152A), but defect sites may become recombination centers and are limited to a single C1 product.

[0005] Therefore, existing TiO2-based catalysts are generally limited to the generation of C1 products: the aforementioned technologies have failed to achieve efficient synthesis of multi-carbon products. The fundamental reason lies in the limitation of their design strategies—either focusing on light absorption and introducing recombination centers, or pursuing selectivity at the expense of charge transport efficiency, or optimizing activation capacity but failing to stabilize the key intermediates required for multi-carbon pathways. This lack of comprehensive control makes it difficult for existing technologies to drive the complex multi-electron reaction processes in CO2 reduction and to break through the C2 product barrier. +Bottlenecks in the production of high value-added products.

[0006] Therefore, developing a novel photoelectrocatalyst that can fundamentally regulate the electronic structure of TiO2, extend its charge lifetime, and enhance CO2 activation and intermediate stabilization is of great significance for achieving the efficient conversion of CO2 into high-value-added organic carbonates. Summary of the Invention

[0007] The purpose of this invention is to overcome the problem that existing TiO2-based catalysts can usually only generate C1 products (such as CO and HCOOH) in photoelectrocatalytic CO2 reduction reactions, making it difficult to achieve highly selective synthesis of multi-carbon products (such as dimethyl carbonate and diethyl carbonate).

[0008] To achieve the above objectives, a first aspect of the present invention provides a composite catalyst for the photoelectrocatalytic reduction of carbon dioxide to prepare organic carbonates, the composite catalyst being formed by combining silver-doped titanium dioxide particles with hydroxylated carbon nanotubes; the structural expression of the composite catalyst is Ag1 / TiO2-(OH)CNTs;

[0009] The silver single atoms replace some of the titanium sites in the titanium dioxide particles through Ag-O-Ti bonds, forming an Ag 4d-O2p orbital hybrid structure.

[0010] A second aspect of the present invention provides a method for preparing the composite catalyst described in the first aspect, the method comprising:

[0011] (1) Titanium dioxide, hydroxylated carbon nanotubes, silver source and solvent are mixed to obtain a suspension;

[0012] (2) The suspension is subjected to photodeposition reaction to deposit silver in the form of single atoms and dope it into the titanium dioxide lattice to obtain the composite catalyst.

[0013] A third aspect of the present invention provides a photoelectrocatalytic system for the preparation of organic carbonates from carbon dioxide, the photoelectrocatalytic system comprising the composite catalyst described in the first aspect.

[0014] A fourth aspect of the present invention provides a method for preparing organic carbonates by photoelectrocatalytic reduction of carbon dioxide, the method comprising:

[0015] In the presence of a photoelectrocatalytic system, carbon dioxide and alcohols undergo a paired electrolytic reaction to obtain the organic carbonate; the electrolysis potential of the paired electrolytic reaction is -1.8 V to -2.6 V.

[0016] The photoelectrocatalytic system contains an electrolyte, which is an alcohol solution containing a halide salt, and the concentration of the electrolyte is 0.1-0.4 mol / L.

[0017] The photoelectrocatalytic system is the photoelectrocatalytic system described in the third aspect.

[0018] The composite catalyst provided by this invention has at least the following advantages:

[0019] 1) Reduction of reaction energy barrier: The hybrid state selectively stabilizes the COOH intermediate, reducing its formation energy barrier from 2.38 eV to 1.22 eV, which greatly improves the CO2 activation efficiency.

[0020] 2) Mass transfer and intermediate stabilization: The (OH)CNTs network provides a high specific surface area and abundant pores. Its surface hydroxyl groups can stabilize methanol-derived -CH3O intermediates through hydrogen bonding, promoting CO overflow and CO coupling.

[0021] 3) Excellent catalytic performance: In a membrane-free paired electrolyzer, this catalyst can achieve direct CO2 synthesis of DMC with a Faraday efficiency of up to 76.5% and a current density of 57.5 mA·cm⁻¹. -2 The performance degradation is small after 10 cycles of the same electrode sheet, and it can be extended to DEC synthesis.

[0022] In summary, the composite catalyst provided by this invention reduces the CO2 activation energy barrier by inducing Ag 4d-O 2p orbital hybridization through Ag single-atom doping; at the same time, it achieves efficient transport and stabilization of reaction intermediates by utilizing a high specific surface area conductive network constructed with hydroxyl-functionalized carbon nanotubes.

[0023] The composite catalyst provided by this invention can directly and selectively convert CO2 into organic carbonates, and has good stability and substrate scalability; it provides a new strategy for the performance innovation of traditional semiconductors and the high-value utilization of CO2. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the composite catalyst CAT-1;

[0025] Figure 2 This is a high-resolution transmission electron microscope image of the composite catalyst CAT-1;

[0026] Figure 3 The image shows the BET characterization diagrams of the composite catalysts CAT-1 and CAT-D2.

[0027] Figure 4 This is an aberration-corrected transmission electron microscope image of the composite catalyst CAT-1;

[0028] Figure 5 This is the near-edge X-ray absorption fine structure spectrum of silver in the composite catalyst CAT-1;

[0029] Figure 6These are the two-dimensional transient absorption spectra of the composite catalysts CAT-1 and CAT-D1;

[0030] Figure 7 This is the X-ray photoelectron spectroscopy of the composite catalyst CAT-1;

[0031] Figure 8 This is the high-resolution X-ray photoelectron spectroscopy of the composite catalyst CAT-1;

[0032] Figure 9 The composite catalyst CAT-1 underwent 10-cycle stability testing in IT mode and 10-cycle FE testing. DMC Data comparison.

[0033] Figure 10 It refers to the energy barrier changes during the catalytic process of the composite catalysts CAT-1 and CAT-D1. Detailed Implementation

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] As previously stated, a first aspect of the present invention provides a composite catalyst for the photoelectrocatalytic reduction of carbon dioxide to prepare organic carbonates, the composite catalyst being formed by combining silver single-atom-doped titanium dioxide particles with hydroxylated carbon nanotubes; the structural expression of the composite catalyst is Ag1 / TiO2-(OH)CNTs;

[0036] The silver single atoms replace some of the titanium sites in the titanium dioxide particles through Ag-O-Ti bonds, forming an Ag 4d-O2p orbital hybrid structure.

[0037] Preferably, based on the mass of the composite catalyst, the loading of silver in the composite catalyst is 0.5-1.5 wt%, preferably 0.5 wt%.

[0038] Preferably, the specific surface area of ​​the composite catalyst is 40-100 m². 2 / g, preferably 65.45 m 2 / g.

[0039] This invention provides a silver-doped TiO2 / hydroxyl-functionalized carbon nanotube composite catalyst with an Ag 4d-O 2p orbital hybrid structure. This composite catalyst can simultaneously achieve broadened light absorption of wide-bandgap semiconductors, extended charge separation lifetime, lowered CO2 activation barrier, and highly efficient stabilization of reaction intermediates, thereby realizing the direct and highly selective synthesis of organic carbonates from CO2 in a membrane-free paired electrolysis system.

[0040] As previously described, a second aspect of the present invention provides a method for preparing the composite catalyst described in the first aspect, the method comprising:

[0041] (1) Titanium dioxide, hydroxylated carbon nanotubes, silver source and solvent are mixed to obtain a suspension;

[0042] (2) The suspension is subjected to photodeposition reaction to deposit silver in the form of single atoms and dope it into the titanium dioxide lattice to obtain the composite catalyst.

[0043] Preferably, the mass ratio of the titanium dioxide to the silver source is 1:0.005-0.025.

[0044] In a preferred embodiment, the mass ratio of the titanium dioxide to the silver source is 1:0.006-0.025.

[0045] Preferably, the mass ratio of titanium dioxide to hydroxylated carbon nanotubes is 1.5-4:1.

[0046] Preferably, the mass ratio of titanium dioxide to hydroxylated carbon nanotubes is 1.5-3:1.

[0047] Preferably, the hydroxylated carbon nanotubes have an outer diameter of 10-20 nm, an inner diameter of 2-8 nm, a length of 10-40 μm, a resistivity of 1500-1800 μΩ·m, and a specific surface area ≥190 m². 2 / g.

[0048] Preferably, the surface of the hydroxylated carbon nanotubes contains -OH functional groups, which can form a three-dimensional conductive network with the titanium dioxide.

[0049] Preferably, the titanium dioxide is anatase titanium dioxide.

[0050] Preferably, the silver source is selected from at least one of silver nitrate, silver sulfate, silver chlorate, and silver perchlorate.

[0051] In a preferred embodiment, the silver source is selected from at least one of silver nitrate, silver sulfate, and silver chlorate.

[0052] Preferably, the solvent is water and / or methanol.

[0053] More preferably, the solvent is a mixture of water and methanol; the volume ratio of water to methanol is 5:1.

[0054] Preferably, based on the amount of hydroxylated carbon nanotubes used being 0.1g, the amount of solvent used is 50-80mL.

[0055] Preferably, the photodeposition reaction is carried out under illumination; the illumination conditions include: illumination wavelength of 350-400nm, illumination intensity of 200-400W, and illumination time of 1-3h.

[0056] More preferably, in the photodeposition reaction, the light source is a xenon lamp.

[0057] As previously described, a third aspect of the present invention provides a photoelectrocatalytic system for the preparation of organic carbonates from carbon dioxide, the photoelectrocatalytic system comprising the composite catalyst described in the first aspect.

[0058] Preferably, in the photoelectrocatalytic system, the composite catalyst serves as the cathode catalyst.

[0059] Preferably, the photoelectrocatalytic system further includes an anode catalyst and an electrolytic cell.

[0060] More preferably, the anode catalyst is Pt.

[0061] More preferably, the electrolytic cell is a membrane-free single-chamber electrolytic cell.

[0062] The composite catalyst provided by this invention can directly and selectively convert CO2 into organic carbonates in a membrane-free paired electrolysis system, and has good stability and substrate scalability; it provides a new strategy for the performance innovation of traditional semiconductors and the high-value utilization of CO2.

[0063] More preferably, the composite catalyst is loaded onto an electrode as a cathode and placed in a membrane-free single-chamber electrolyzer.

[0064] More preferably, the operation of loading the composite catalyst on the electrode is as follows: the composite catalyst and the dispersion solution are mixed, ultrasonically prepared to obtain a slurry, then coated onto hydrophobic carbon paper, and dried to obtain a cathode.

[0065] More preferably, the amount of the composite catalyst is 8-12 mg relative to 520 μL of dispersion solution.

[0066] More preferably, the dispersion solution contains alcohols and Nafion solution.

[0067] More preferably, the hydrophobic carbon paper has a size of 1.3 × 1.5 cm. 2 .

[0068] More preferably, the photoelectrocatalytic system further contains a Pd / C cocatalyst; the amount of the Pd / C cocatalyst is 0-200 mg. In this preferred embodiment, the Pd / C cocatalyst can promote the coupling reaction between CO and alkoxy groups.

[0069] As previously described, a fourth aspect of the present invention provides a method for preparing organic carbonates by photoelectrocatalytic reduction of carbon dioxide, the method comprising:

[0070] In the presence of a photoelectrocatalytic system, carbon dioxide and alcohols undergo a paired electrolytic reaction to obtain the organic carbonate; the electrolysis potential of the paired electrolytic reaction is -1.8 V to -2.6 V.

[0071] The photoelectrocatalytic system contains an electrolyte, which is an alcohol solution containing a halide salt, and the concentration of the electrolyte is 0.1-0.4 mol / L.

[0072] The photoelectrocatalytic system is the photoelectrocatalytic system described in the third aspect.

[0073] In this invention, the electrolysis potential is the potential value relative to the Ag / AgCl reference electrode.

[0074] Preferably, the carbon dioxide is a carbon source.

[0075] Preferably, the alcohol is methanol and / or ethanol. In this preferred embodiment, the alcohol serves as both a reaction medium and a reactant.

[0076] Preferably, Nafion solution is also added to the paired electrolysis reaction.

[0077] Preferably, the volume ratio of the alcohol to the Nafion solution is 10-12:1.

[0078] In this invention, the Nafion solution refers to a dispersion of perfluorosulfonic acid resin (PFSA) in a mixed solvent of water and low-carbon alcohol (not a traditional true solution, containing micro-aggregates), with the core value being strong proton conduction, chemical stability, and resistance to acids and solvents.

[0079] In a preferred embodiment, the organic carbonate is dimethyl carbonate and / or diethyl carbonate.

[0080] Preferably, the electrolyte is selected from at least one of a methanol solution of sodium bromide, an ethanol solution of sodium bromide, a methanol solution of potassium bromide, and an ethanol solution of potassium bromide.

[0081] Preferably, the electrolyte is selected from at least one of sodium bromide methanol solution, sodium bromide aqueous solution, and potassium bromide methanol solution.

[0082] Preferably, the paired electrolysis reaction is carried out under light irradiation, and the wavelength of the light irradiation is 380 nm or 510 nm.

[0083] More preferably, in the paired electrolysis reaction, the light source for illumination is a light-emitting diode (LED) light source.

[0084] The present invention will be described in detail below through embodiments. Unless otherwise specified, all instruments and materials used in the following embodiments are commercially available products.

[0085] The room temperature or normal temperature mentioned in this article means 25±2℃.

[0086] Anatase titanium dioxide: purchased from Aladdin Reagents (Shanghai) Co., Ltd.

[0087] Hydroxylated carbon nanotubes I: outer diameter 10 nm, inner diameter 3 nm, length 20 μm, resistivity 1500 μΩ·m, specific surface area 210 m² / m³. 2 / g, purchased from Shenzhen Suiheng Technology Co., Ltd.

[0088] Hydroxylated carbon nanotubes II: outer diameter 20 nm, inner diameter 10 nm, length 10 μm, resistivity 2000 μΩ·m, specific surface area 190 m² / m². 2 / g, purchased from Shenzhen Suiheng Technology Co., Ltd.

[0089] Silver nitrate: purity 99.95 wt%, purchased from Tianjin Tiangan Chemical Technology Development Co., Ltd.

[0090] Hydrophobic carbon paper: 1.3 × 1.5 cm 2 Purchased from Toray Industries, Inc.

[0091] NaBr: purity 99.99 wt%, purchased from Maclean's Reagent Company.

[0092] CH3OH: purity 99.9 wt%, purchased from Adamas.

[0093] Pd / C co-catalyst: purchased from Adamas.

[0094] Example 1: Preparation of composite catalyst

[0095] (1) Titanium dioxide powder, hydroxylated carbon nanotubes and silver nitrate (i.e., silver source, so that the final Ag element loading is 0.5 wt%) were dispersed in 60 mL of a mixed solvent containing water and methanol (the volume ratio of water and methanol is 5:1), ultrasonically dispersed for 30 min, and magnetically stirred for 30 min to make them uniformly mixed and obtain a uniform suspension.

[0096] (2) Place the suspension under a 300 W xenon lamp light source to irradiate it and carry out photodeposition reaction until the system changes from light gray to gray-black, so that silver is deposited in the form of single atoms and doped into the titanium dioxide lattice.

[0097] After the reaction was completed, the product was centrifuged (6000 rpm for 10 min), washed three times each with deionized water and ethanol, dried in an oven at 80 ℃ for 8 h, and ground to obtain Ag1 / TiO2-(OH)CNTs composite catalyst powder, named CAT-1.

[0098] The specific raw material usage and process parameters for this embodiment are shown in Table 1.

[0099] Examples 2-4

[0100] The same process as in Example 1 was used, except that the amount of raw materials or process parameters were different, as shown in Table 1.

[0101] Table 1

[0102]

[0103] Comparative Example 1

[0104] The same procedure as in Example 1 was used, except that silver nitrate was not added in this comparative example. All other steps were the same as in Example 1. Specifically,

[0105] Titanium dioxide powder and hydroxylated carbon nanotubes I were dispersed in a mixed solvent containing water and methanol (volume ratio of water to methanol was 5:1), ultrasonically dispersed for 30 min, and magnetically stirred for 30 min to achieve uniform mixing and obtain a uniform suspension.

[0106] After the reaction was completed, the product was centrifuged (6000 rpm for 10 min), washed three times each with deionized water and ethanol, dried in an oven at 80 °C for 8 h, and ground to obtain Ag-free TiO2-(OH)CNTs catalyst powder, named CAT-D1.

[0107] Comparative Example 2

[0108] The same procedure as in Example 1 was used, except that hydroxyl-functionalized carbon nanotubes were not added in this comparative example. All other steps were the same as in Example 1. Specifically,

[0109] (1) Disperse titanium dioxide powder and silver nitrate (i.e., silver source, so that the final Ag element loading is 0.5wt%) in a mixed solvent containing water and methanol (the volume ratio of water and methanol is 5:1), ultrasonically disperse for 30 min, and magnetically stir for 30 min to make them uniformly mixed and obtain a uniform suspension.

[0110] (2) Place the suspension under a 300 W xenon lamp light source to irradiate it and carry out photodeposition reaction until the system changes from light gray to gray-black, so that silver is deposited in the form of single atoms and doped into the titanium dioxide lattice.

[0111] After the reaction was completed, the product was centrifuged (6000 rpm for 10 min), washed three times each with deionized water and ethanol, dried in an oven at 80 °C for 8 h, and ground to obtain Ag1 / TiO2 catalyst powder without (OH)CNTs, which was named CAT-D2.

[0112] Comparative Example 3

[0113] The same procedure as in Example 1 was used, except that in this comparative example, Ag nanoparticles were loaded onto TiO2-(OH)CNTs using a chemical reduction method. Specifically,

[0114] (1) Titanium dioxide powder, hydroxylated carbon nanotubes I and silver nitrate (i.e., silver source, so that the final Ag element loading is 0.5wt%) were dispersed in a mixed solvent containing water and methanol (the volume ratio of water and methanol is 5:1), ultrasonically dispersed for 30 min, and magnetically stirred for 30 min to make them uniformly mixed and obtain a uniform suspension.

[0115] (2) Add excess sodium hydroxide solution to the suspension to carry out a chemical precipitation reaction. Stir thoroughly to allow silver to be deposited and doped into the titanium dioxide lattice.

[0116] After the reaction was complete, the product was centrifuged (6000 rpm for 10 min), washed three times each with deionized water and ethanol, dried in an oven at 80 °C for 8 h, and the Ag obtained after grinding was... NP / TiO2-(OH)CNTs catalyst powder, named CAT-D3.

[0117] Preparation Example 1: Preparation of dimethyl carbonate (DMC) by photoelectrochemical reduction of carbon dioxide

[0118] 10 mg of the composite catalyst CAT-1 prepared in Example 1 was dispersed in 475 μL of ethanol (i.e., alcohol) and 45 μL of Nafion solution, and ultrasonically prepared into a slurry. The slurry was then uniformly coated onto hydrophobic carbon paper (1.3 × 1.5 cm). 2 The cathode working electrode is dried at room temperature.

[0119] The electrolytic cell is a membrane-free, single-chamber type, containing a 0.2 mol / L NaBr-CH3OH solution (i.e., the electrolyte), with CO2 continuously introduced. A voltage of -2.4 V is applied at the cathode. vsThe cathode was irradiated with a 380 nm LED light source at the Ag / AgCl electrolysis potential. 100 mg of Pd / C was added to the anode (Pt) chamber as a co-catalyst to prepare dimethyl carbonate (i.e., an organic carbonate).

[0120] After 1 h of reaction, the liquid product was injected into a gas chromatograph and analyzed by GC-MS. The Faraday efficiency and current density were determined, and the performance test results are shown in Table 3.

[0121] Preparation Examples 2-7

[0122] The same process as in Preparation Example 1 was used, except that the type of composite catalyst was different, as shown in Table 2. The performance test results are shown in Table 3.

[0123] Table 2

[0124]

[0125] Preparation Example 8: Preparation of diethyl carbonate (DEC) by photoelectrocatalytic reduction of carbon dioxide

[0126] The same procedure as in Preparation Example 1 was used, except that in this preparation example, methanol in the solution was replaced with an equal volume of anhydrous ethanol. The reaction product was identified as diethyl carbonate (DEC) by GC-MS. The remaining steps were the same as in Preparation Example 1. The performance test results are shown in Table 3.

[0127] The formula for calculating Faraday efficiency is:

[0128] in, V This is the volume concentration of CO, expressed in ppm. v The flow rate of CO2 is expressed in mL / min. i This is a constant current, measured in amperes (A).

[0129] Table 3

[0130]

[0131] As can be seen from the results in Table 3, under the same test conditions, the DMC Faradaic efficiency of TiO2-(OH)CNTs without Ag doping (Preparation Example 5) is only 40.7%, and the CO Faradaic efficiency is less than 45%; the DMC Faradaic efficiency of Ag1 / TiO2 without (OH)CNTs (Preparation Example 6) is 40.5%, and the current density is significantly reduced; Ag nanoparticle-loaded Ag NP The DMC Faradaic efficiency of / TiO2-(OH)CNTs (Preparation Example 7) was only 48.2%, and the stability was poor.

[0132] Test Example 1: Characterization of Composite Catalyst Structure

[0133] The composite catalyst prepared in Example 1 was characterized.

[0134] The present invention provides, exemplarily, scanning electron microscope images of the composite catalyst CAT-1, such as... Figure 1 As shown, from Figure 1 As can be seen, the scanning electron microscopy (SEM) results clearly demonstrate the overall microstructure of the catalyst. The sample surface is uniformly distributed with intertwined carbon nanotubes and white particulate components, collectively constructing a loose, porous, and rough-surfaced composite structure. This intertwined morphology is not simply a physical blend, but rather a structural design centered on catalytic performance: Firstly, the interlocking carbon nanotubes form a continuous, interconnected three-dimensional framework, providing stable anchoring points for the nucleation and growth of silver single atoms and the uniform dispersion of TiO2 nanoparticles, significantly inhibiting the aggregation of TiO2 during high-temperature preparation or catalytic reactions; secondly, the rough, porous surface effectively increases the specific surface area of ​​the catalyst, providing abundant gas-solid reaction interfaces for the adsorption and transport of CO2 molecules. This advantage can be directly translated into a larger electrochemical active area, providing a good mass transfer basis for the CO2 electrocatalytic reduction process.

[0135] This invention provides, exemplarily, a high-resolution transmission electron microscope image of the composite catalyst CAT-1, such as... Figure 2 As shown, from Figure 2 As can be seen, high-resolution transmission electron microscopy (HRTEM) characterization further elucidated the fine crystal structure of the catalyst, clearly identifying two sets of characteristic interplanar spacings of 0.350 nm and 0.333 nm, which belong to the (101) crystal plane of anatase TiO2 and the (002) crystal plane of carbon nanotubes (CNTs), respectively. The accurate determination of the interplanar spacing is crucial for structural indicative significance: the standard interplanar spacing of the anatase TiO2 (101) crystal plane is 0.352 nm, while the 0.350 nm measured in this experiment shows a slight shrinkage. This subtle difference can be attributed to the local lattice distortion induced by the introduction of Ag single atoms, confirming from a crystallographic microscopic level the strong interaction between Ag single atoms and the TiO2 matrix.

[0136] This invention provides, by way of example, BET characterization diagrams of composite catalysts CAT-1 and CAT-D2, as shown below. Figure 3 As shown, from Figure 3 It can be seen that the specific surface area of ​​the Ag1 / TiO2-(OH) CNTs composite material can reach 65.45 m². 2 / g, compared with Ag1 / TiO2 without the introduction of (OH)CNTs (only 10.45 m 2Compared to ( / g), the improvement is nearly 6 times. This significant improvement is not solely due to carbon nanotubes, but rather the result of the synergistic construction of (OH)CNTs and TiO2: on the one hand, (OH)CNTs themselves have a high specific surface area, serving as an excellent porous support framework; on the other hand, their three-dimensional interconnected network can effectively separate TiO2 nanocrystals, inhibiting their aggregation during the preparation process, thereby preserving a rich microporous and mesoporous system, providing a large number of usable sites for the adsorption, diffusion, and interfacial mass transfer of CO2 molecules.

[0137] This invention provides, exemplarily, aberration-corrected transmission electron microscopy (TEM) images of the composite catalyst CAT-1, such as... Figure 4 As shown, from Figure 4 As can be seen from the aberration-corrected transmission electron microscopy (AC-TEM) images, a large number of independently distributed bright spots (circled in cyan) can be clearly observed. These isolated bright spots are silver single-atom sites, and no silver-based nanoparticles or clusters were detected in the images. Statistical results show that silver single atoms are uniformly distributed on the support surface, without local aggregation or clustering regions. This phenomenon directly proves that the photodeposition method used in this study has excellent controllability and stability: the mild photoreduction reaction conditions can precisely control the nucleation and growth of silver, effectively suppressing the single-atom migration and aggregation problems that easily occur in high-temperature or strong reduction systems, and achieving high dispersion of silver single atoms in the TiO2 matrix. This atomically dispersed structure is of great significance for improving catalytic performance: highly dispersed silver single atoms have a high atomic utilization rate, which can maximize the exposure of catalytic active centers, while eliminating the size effect and crystal plane difference interference caused by the presence of nanoparticles or clusters.

[0138] This invention provides, by way of example, a fine structure map of the near-edge X-ray absorption spectra of silver in the composite catalyst CAT-1, such as... Figure 5 As shown, from Figure 5 It can be seen that only Ag-O coordination peaks and no Ag-Ag metallic bond peaks appear in the near-edge X-ray absorption fine structure spectrum of silver, confirming that Ag exists in a non-metallic state; at the same time, Ag-Ti scattering paths are detected, indicating that Ag enters the TiO2 lattice.

[0139] This invention provides, by way of example, two-dimensional transient absorption spectra of composite catalysts CAT-1 and CAT-D1, such as... Figure 6 As shown, from Figure 6It can be seen that the Ag1 / TiO2-(OH)CNTs composite material exhibits a significant enhancement in excited-state absorption signal in the 375nm-400nm violet region, while pure TiO2-(OH)CNTs show virtually no response in this range. This enhancement is directly attributed to the formation of the Ag 4d-O 2p hybrid state. This hybrid state introduces a new energy level into the band gap, providing an additional relaxation path for excited-state electrons, enabling previously difficult-to-observe electronic transitions to become apparent. Simultaneously, it effectively broadens the material's light absorption range, which is consistent with the UV-vis DRS results, and also increases the initial concentration of photogenerated carriers.

[0140] The present invention provides, by way of example, the X-ray photoelectron spectroscopy of the composite catalyst CAT-1, such as... Figure 7 As shown, from Figure 7 It can be seen that only Ti 2p, Ag 3d, O 1s and C 1s characteristic peaks appeared on the surface of the Ag1 / TiO2-(OH)CNTs catalyst, with no other impurity signals, proving that the sample has high chemical purity. Among them, the C 1s signal originates from the hydroxylated carbon nanotube support, the Ti 2p and O 1s signals mainly come from TiO2, and the presence of the Ag 3d signal directly confirms that the silver species have been successfully loaded, providing a basis for subsequent high-resolution XPS fine chemical state analysis.

[0141] This invention provides, by way of example, a high-resolution X-ray photoelectron spectroscopy of the composite catalyst CAT-1, such as... Figure 8 As shown, the high-resolution XPS spectrum of Ag 3d ( Figure 8 From a), we can see that Ag 3d in the sample 5 / 2 With 3D 3 / 2 The binding energies are 368.26 eV and 374.16 eV, respectively, and the spin-orbit splitting energy is 6.0 eV, consistent with the characteristics of metallic Ag. Compared with the standard binding energy of Ag foil (368.0 eV), Ag 3d... 5 / 2 The binding energy shows a positive shift of 0.26 eV, indicating that the Ag atom is in an electron-deficient state, in a partially oxidized zero-valence state (Ag0 / δ). + The presence of ) is consistent with the result that the absorption edge position in the Ag K-edge XANES spectrum (Figure 5) is between Ag foil and Ag2O, further confirming that the average valence state of Ag is between 0 and +1.

[0142] Ti 2p high-resolution XPS spectrum ( Figure 8 b) provides direct evidence for charge transfer within the system, Ti 2p 3 / 2 With 2p 1 / 2The binding energies were 458.73 eV and 464.41 eV, respectively, showing a negative shift of 0.3 eV compared to the TiO2 standard, indicating a significant increase in the electron density at Ti sites; peak fitting showed that Ti in the system... 3+ The proportion reaches 19%, forming a clear charge balance with the electron deficiency at Ag sites. These results indicate that electrons can transfer from Ag to Ti sites through the Ag-O-Ti interface bonding structure, promoting the transfer of electrons from Ag to Ti sites. 4+ Partially restored to Ti 3+ This demonstrates significant electronic metal-carrier interaction (EMSI) and provides experimental evidence for the Ag→Ti ​​charge transfer path predicted by DFT calculations.

[0143] O 1s high-resolution XPS spectrum ( Figure 8 The fitting results in c) show that the sample exhibits characteristic peaks of lattice oxygen, oxygen vacancies, and hydroxyl oxygen at 530.33 eV, 532.07 eV, and 535.39 eV, respectively. Among them, the relative content of oxygen vacancies reaches 18%, which can be attributed to Ag with a larger ionic radius. + Replace Ti 4+ This induces lattice distortion and local expansion in TiO2, which in turn promotes the detachment of some lattice oxygen to form oxygen vacancies. The presence of oxygen vacancies can not only serve as photogenerated electron trapping sites to suppress carrier recombination, but also provide abundant defect active centers for CO2 adsorption and activation.

[0144] In addition, the C 1s high-resolution XPS spectrum ( Figure 8 d) confirms the presence of sp² hybrid carbon, hydroxyl carbon, and carboxyl carbon on the surface of (OH)CNTs, with the C-OH component accounting for approximately 28%, indicating that the hydroxyl functional groups on the carbon nanotube surface are sufficiently modified, providing good support for the interfacial structure and dispersibility of the catalyst.

[0145] Test Example 2: Stability Test

[0146] Under the conditions of Preparation Example 1, the same electrode sheet was subjected to 10 consecutive cycle stability tests using an electrochemical workstation in IT mode. Sampling and data acquisition were performed for each cycle (e.g., ...). Figure 9 (As shown). Figure 9 The results showed that the catalyst exhibited good stability during multiple cyclic electrolysis processes, with the DMC Faraday efficiency gradually decreasing from an initial 76.5% to 68.3%, and the current density decreasing from 57.5 mA. cm -2 It slowly decayed to 51.7mA. cm -2 The overall attenuation is small, and the cycle performance is excellent.

[0147] Test Example 3: Reaction Energy Barrier

[0148] The testing method is: DFT calculation (VASP).

[0149] Based on density functional theory and the projected-added plane wave method, the VASP program is used, considering spin polarization. The exchange-correlated functional is PBE-GGA, and DFT-D3 correction of van der Waals interactions is employed. The plane wave cutoff energy is 450 eV, and the energy convergence accuracy is 1×10⁻⁶. -5 eV, electron broadening 0.03 eV (Gaussian broadening). Structure optimization was performed using a 2×2×1 k-point grid, density of states calculation was performed using a 4×4×1 grid, and atomic residual forces converged to <0.02 eV / Å.

[0150] Free energy calculation: For adsorbed species, G = E + Gcor, T = 298.15 K, where Gcor is obtained from frequency calculations + Vaspkit. The proton-electron pair free energy is taken as 1 / 2 G(H2). The thermodynamic quantities of gaseous molecules are calculated from zero-point energy, thermal correction, and entropy terms. The partial pressures of H2 / CO2 / CO are 1 atm, and H2O(l) is 0.035 bar. The spin multiplicity of all of them is 1.

[0151] Test results are as follows Figure 10 As shown, through quantitative analysis of the reaction energy barrier, the rate-determining step of the CO2 reduction reaction and the core regulatory role of Ag doping were clarified. Calculations show that the activation of CO2 to generate *COOH is the rate-determining step of CO2 reduction to CO, and its energy barrier directly determines the reaction rate. The free energy barrier of this step on the TiO2-(OH)CNTs (CAT-D1) surface is as high as 2.38 eV, consistent with its relatively weak CO2 activation ability. This also explains the low intensity of the *COOH characteristic peak in the DRIFTTS experiment from a thermodynamic perspective—the high energy barrier makes it difficult for intermediates to form and easily decomposes, making effective enrichment impossible. After Ag atom doping (CAT-1), the rate-determining step energy barrier was significantly reduced to 1.22 eV, a decrease of 48.7%, and the thermodynamic feasibility was significantly improved.

[0152] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite catalyst for the photoelectrocatalytic reduction of carbon dioxide to prepare organic carbonates, characterized in that, The composite catalyst is formed by combining silver-doped titanium dioxide particles with hydroxylated carbon nanotubes; the structural formula of the composite catalyst is Ag1 / TiO2-(OH)CNTs; Based on the mass of the composite catalyst, the loading of silver in the composite catalyst is 0.5-1.5 wt%; in the method for preparing the composite catalyst, the mass ratio of titanium dioxide to hydroxylated carbon nanotubes is 1.5-4:

1. The silver single atoms replace some of the titanium sites in the titanium dioxide particles through Ag-O-Ti bonds, forming an Ag 4d-O 2p orbital hybrid structure.

2. The composite catalyst according to claim 1, characterized in that, The specific surface area of the composite catalyst is 40-100 m 2 / g.

3. A method for preparing the composite catalyst according to claim 1 or 2, characterized in that, The method includes: (1) Titanium dioxide, hydroxylated carbon nanotubes, silver source and solvent are mixed to obtain a suspension; the mass ratio of titanium dioxide to silver source is 1:0.005-0.025; the mass ratio of titanium dioxide to hydroxylated carbon nanotubes is 1.5-4:1; (2) The suspension is subjected to photodeposition reaction to deposit silver in the form of single atoms and dope it into the titanium dioxide lattice to obtain the composite catalyst.

4. The method according to claim 3, characterized in that, The hydroxylated carbon nanotube has an outer diameter of 10-20 nm, an inner diameter of 2-8 nm, a length of 10-40 μm, a resistivity of 1500-1800 μΩ.m, and a specific surface area of ≥190 m 2 / g. And / or, the silver source is selected from at least one of silver nitrate, silver chlorate, and silver perchlorate; And / or, the solvent is water and / or methanol.

5. The method according to claim 3 or 4, characterized in that, The photodeposition reaction is carried out under illumination; the illumination conditions include: illumination wavelength of 350-400nm, illumination intensity of 200-400W, and illumination time of 1-3h.

6. A photoelectrocatalytic system for the preparation of organic carbonates from carbon dioxide, characterized in that, The photoelectrocatalytic system contains the composite catalyst as described in claim 1 or 2.

7. A method for preparing organic carbonates by photoelectrocatalytic reduction of carbon dioxide, characterized in that, The method includes: In the presence of a photoelectrocatalytic system, carbon dioxide and alcohols undergo a paired electrolytic reaction to obtain the organic carbonate; the electrolysis potential of the paired electrolytic reaction is -1.8 V to -2.6 V. The photoelectrocatalytic system contains an electrolyte, which is an alcohol solution containing a halide salt, and the concentration of the electrolyte is 0.1-0.4 mol / L. The photoelectrocatalytic system is the photoelectrocatalytic system described in claim 6.

8. The method according to claim 7, characterized in that, The alcohols are methanol and / or ethanol; And / or, the organic carbonate is dimethyl carbonate and / or diethyl carbonate; And / or, the electrolyte is selected from at least one of a methanol solution of sodium bromide, an ethanol solution of sodium bromide, a methanol solution of potassium bromide, and an ethanol solution of potassium bromide.

9. The method according to claim 7 or 8, characterized in that, The paired electrolysis reaction is carried out under illumination, with the wavelength of the illumination being 380 nm or 510 nm.

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