A Bi@Ce-UiO-66-Br catalyst and its photocatalytic reduction of CO 2 Application

Abstract

This invention discloses a Bi@Ce-UiO-66-Br catalyst and its photocatalytic reduction of CO. 2 In this application, the catalyst is prepared by a solvothermal method using a ligand-functionalized Ce-based metal-organic framework (Ce-UiO-66-Br), followed by in-situ reduction encapsulation to confine and encapsulate metallic Bi within Ce-UiO-66-Br, forming a core-shell structured photocatalyst. The Ce-UiO-66-Br shell provides spatial confinement and dispersion stability for the metallic Bi, while the Bi core and the Ce-UiO-66-Br shell produce a synergistic catalytic effect, precisely controlling CO2 emissions. 2 The reduction reaction pathway directs the reaction to produce CH4. 4 The catalyst of this invention has a simple and highly controllable preparation process, and the resulting catalyst has a stable structure. It also exhibits photocatalytic CO2 production under simulated sunlight. 2 Reduction of CH 4 The selectivity is nearly 90%, and the photocatalytic stability is excellent; this catalyst can be directly applied to gas / liquid phase photocatalytic CO2 production. 2 The reducing system is CO. 2 Highly selective conversion of CH 4 It provides highly efficient core materials, which have both academic research value and industrial application prospects.

Description

A Bi@Ce-UiO-66-Br catalyst and its application in photocatalytic reduction of CO2 Technical Field

[0001] This invention belongs to the field of photocatalytic material preparation and carbon dioxide (CO2) resource utilization technology. Specifically, it relates to a ligand-functionalized Ce-based metal-organic framework (Ce-UiO-66-Br) Bi metal core-shell photocatalyst, and the application of this catalyst in the highly selective photocatalytic reduction of CO2 to methane under simulated sunlight. This catalyst can be directly used in gas-phase / liquid-phase photocatalytic CO2 conversion to clean energy fuel systems. Background Technology

[0002] Photocatalytic CO2 reduction technology has become a highly promising CO2 resource recovery technology due to its mild reaction conditions and the use of clean solar energy. This technology converts light energy into chemical energy through a photocatalyst, driving the reduction of CO2 with a proton source to generate various high-value products, thus achieving a closed-loop carbon cycle. However, this reaction suffers from bottlenecks such as poor product selectivity and insufficient catalyst stability, making it difficult to meet the requirements of industrial applications. Therefore, developing photocatalytic materials with high activity, high selectivity, and long-term cycle stability is currently a core research topic in this field.

[0003] Existing photocatalytic CO2 reduction catalyst systems mainly include elemental metals, metal oxides, nitrides, metal-organic frameworks (MOFs), and carbon-based composite materials. Among them, bismuth (Bi)-based materials have become a research hotspot in this field due to their suitable band structure, efficient absorption of visible light, adsorption and activation capabilities for CO2, high abundance in the Earth's crust, and environmental friendliness. However, pure Bi or simple Bi-based compounds have significant drawbacks as photocatalysts: rapid recombination of photogenerated electron-hole pairs, low quantum efficiency, and poor catalytic activity; lack of CO2-specific adsorption sites on the surface, resulting in poor product selectivity; and the low melting point of Bi, leading to easy particle agglomeration and deactivation, which severely restricts their long-term practical application.

[0004] Metal-organic frameworks (MOFs) are ideal supports for encapsulating metal-based catalysts into core-shell structures due to their high specific surface area, tunable pore structure, and abundant active sites. Ce-UiO-66, in particular, relies on Ce... 3+ / Ce 4+ The reversible valence state transition of Ce can effectively promote photogenerated charge transfer, and its framework structure can also provide good dispersion for the metal core. However, existing Ce-based MOF photocatalysts still have technical bottlenecks: limited CO2 adsorption and activation capacity, making it difficult to improve reduction selectivity; weak bonding force between the metal core and shell interface, low charge transfer efficiency, affecting the stability of catalytic performance. Summary of the Invention

[0005] To address the shortcomings of existing photocatalytic CO2 reduction catalysts, such as low CH4 selectivity, high photogenerated carrier recombination rate, easy catalyst aggregation, and easy deactivation of active sites, this invention provides a Ce-UiO-66-Br-encapsulated Bi metal core-shell catalyst (Bi@Ce-UiO-66-Br catalyst). When used in photocatalytic CO2 reduction reactions, this catalyst exhibits high CO2 reduction activity, CH4 selectivity, and good cycle stability.

[0006] The Bi@Ce-UiO-66-Br catalyst provided by the present invention consists of a metallic Bi core and a Ce-UiO-66 shell that is functionalized with Br-based ligands and encapsulates the metallic Bi core; wherein, based on the total mass of the catalyst, the mass percentage of metallic Bi is 25% to 40%, preferably 35%.

[0007] The Bi@Ce-UiO-66-Br catalyst of the present invention is prepared by the following steps:

[0008] Step 1: Dissolve 2-bromoterephthalic acid in N,N-dimethylformamide and dissolve cerium ammonium nitrate in deionized water. Then mix the two solutions and stir at 80-120 °C for 20-60 minutes. After the reaction is complete, wash the solid generated with N,N-dimethylformamide and acetone in sequence, and dry to obtain Br-ligand-functionalized Ce-UiO-66.

[0009] Step 2: Dissolve bismuth nitrate in acetone by sonication, add Br-functionalized Ce-UiO-66, stir at room temperature for 8-12 hours, centrifuge, wash the solid with anhydrous ethanol, and dry under vacuum to obtain the precursor Bi@Ce-UiO-66-Br.

[0010] Step 3: Add the precursor Bi@Ce-UiO-66-Br to ethanol, stir until homogeneous, then add sodium borohydride, stir at room temperature for 5-30 minutes, centrifuge, and wash the solid sequentially with anhydrous methanol and anhydrous ethanol to obtain the catalyst.

[0011] In step 1 above, the preferred molar ratio of 2-bromoterephthalic acid and cerium ammonium nitrate is 1:1.4 to 1:1.6.

[0012] In step 1 above, the volume ratio of deionized water to N,N-dimethylformamide is preferably 1:3 to 1:4.

[0013] Furthermore, in step 1 above, it is preferable to stir the reaction at 100°C for 30 to 40 minutes.

[0014] In step 3 above, the amount of sodium borohydride added is preferably 8 to 13 times the molar amount of Bi in the precursor Bi@Ce-UiO-66-Br.

[0015] The present invention also provides the use of the above-mentioned Bi@Ce-UiO-66-Br catalyst for photocatalytic reduction of CO2 to CH4.

[0016] The beneficial effects of this invention are as follows:

[0017] 1. This invention first prepares ligand-functionalized Ce-UiO-66-Br via a solvothermal method. Functional modification of Ce-UiO-66 with Br-based ligands introduces functional groups that enhance CO2 adsorption and activation, improving CO2 adsorption selectivity. Then, an in-situ reduction encapsulation method is used to confine and stably disperse metallic Bi within the Ce-UiO-66-Br shell, forming a tightly bound core-shell composite photocatalyst. This constructs a highly efficient charge transfer interface, promoting photogenerated electron migration and inhibiting carrier recombination. A synergistic catalytic effect is generated between the Bi core and shell, thereby precisely controlling the CO2 reduction pathway to directionally generate CH4. Simultaneously, the structural stability and reproducibility of the catalyst are improved, providing a promising catalytic material for the highly selective conversion of CO2 to CH4.

[0018] 2. The catalyst of this invention has a simple preparation process, mild conditions, high controllability, and is easy to scale up for production. The obtained catalyst has uniform morphology, stable structure, good catalytic performance, and high environmental compatibility. Under simulated sunlight irradiation, this catalyst exhibits high CO2 reduction activity and CH4 selectivity in the photocatalytic CO2 reduction reaction, with a CH4 selectivity approaching 90%, and demonstrates good catalytic stability. This catalyst is suitable for gas / liquid phase photocatalytic CO2 reduction systems and has promising applications in the field of CO2 resource conversion to CH4. Attached Figure Description

[0019] Figure 1 shows the XRD patterns of the catalysts prepared in Examples 1-3, Ce-UiO-66-Br prepared in Example 1, and BiNPs prepared in Comparative Example 1.

[0020] Figure 2 shows the Fourier transform infrared spectra of the catalysts prepared in Examples 1-3 and Ce-UiO-66-Br prepared in Example 1.

[0021] Figure 3 shows electron microscope images of the Ce-UiO-66-Br and 35BiNP@CUB catalysts prepared in Example 1, where a is a transmission electron microscope (TEM) image of 35BiNP@CUB; b is a high-resolution transmission electron microscope (HRTEM) image of 35BiNP@CUB; c is a scanning electron microscope (SEM) image of Ce-UiO-66-Br; d is a scanning transmission electron microscope (STEM) image of 35BiNP@CUB in dark field mode; e is an elemental energy scattering surface scanning (EDSMapping) image of 35BiNP@CUB; and f is a SEM image of 35BiNP@CUB.

[0022] Figure 4 shows the reduction of CO2 to CH4 and the amount of CO generated by the catalysts prepared in Examples 1-4 and Comparative Examples 1-2 under simulated sunlight, as well as the Ce-UiO-66-Br prepared in Example 1.

[0023] Figure 5 shows the electron utilization rates of the catalysts prepared in Examples 1-4 and Comparative Examples 1-2, and Ce-UiO-66-Br prepared in Example 1, under simulated sunlight.

[0024] Figure 6 shows the amount of CH4 generated in three cycles of the catalysts prepared in Examples 1-4 and Comparative Example 2.

[0025] Figure 7 shows the CO production in three cycles of the catalysts prepared in Examples 1-4 and Comparative Example 2.

[0026] Figure 8 shows the XRD patterns of the 35BiNP@CUB catalyst prepared in Example 1 before and after three cycles of reaction.

[0027] Figure 9 shows the theoretical calculation of the adsorption capacity of Ce-UiO-66 with different ligand modifications for CO2 and CH4. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to these embodiments.

[0029] Example 1

[0030] Step 1: Dissolve 733 mg (2.26 mmol) of 2-bromoterephthalic acid in 16.8 mL of DMF, and dissolve 1.776 g (3.22 mmol) of cerium ammonium nitrate in 5.4 mL of deionized water. After complete dissolution, mix the two solutions, heat to 100 °C, and stir for 30 minutes. After the reaction is complete, wash the resulting solid powder successively with DMF (20 mL × 2 times) and acetone (20 mL × 2 times), and dry in air at 70 °C for 6 hours to obtain Ce-UiO-66-Br.

[0031] Step 2: Dissolve 121.3 mg (0.25 mmol) bismuth nitrate pentahydrate in 25 mL of acetone by sonication, add 100 mg Ce-UiO-66-Br, stir at room temperature for 12 hours, centrifuge, wash the solid three times with anhydrous ethanol, and dry under vacuum at 50 °C for 6 hours to obtain the precursor Bi@Ce-UiO-66-Br.

[0032] Step 3: The precursor Bi@Ce-UiO-66-Br was added to 20 mL of ethanol and stirred for 15 minutes. Then, 100 mg (2.64 mmol) of sodium borohydride was added, and the mixture was stirred at room temperature for 10 minutes. After centrifugation, the solid was washed successively with anhydrous methanol (10 mL × 3 times) and anhydrous ethanol (10 mL × 3 times) to remove excess sodium borohydride and byproducts, yielding the Ce-UiO-66-Br-coated Bi metal core-shell catalyst. Based on the total mass of the obtained catalyst, the mass percentage of metallic Bi was 35%, denoted as 35BiNPs@CUB.

[0033] Example 2

[0034] In step 2 of this embodiment, 145.5 mg (0.3 mmol) of bismuth nitrate pentahydrate was ultrasonically dissolved in 25 mL of acetone, and 100 mg of Ce-UiO-66-Br was added. The mixture was stirred at room temperature for 12 hours, centrifuged, and the solid was washed three times with anhydrous ethanol and then dried under vacuum at 50°C for 6 hours to obtain the precursor Bi@Ce-UiO-66-Br. The other steps were the same as in Example 1, resulting in a Ce-UiO-66-Br-coated Bi metal core-shell catalyst. Based on the total mass of the obtained catalyst, the mass percentage of metallic Bi was 40%, denoted as 40BiNPs@CUB.

[0035] Example 3

[0036] In step 2 of this embodiment, 97 mg (0.2 mmol) of bismuth nitrate pentahydrate was ultrasonically dissolved in 25 mL of acetone, and 100 mg of Ce-UiO-66-Br was added. The mixture was stirred at room temperature for 12 hours, centrifuged, and the solid was washed three times with anhydrous ethanol and then dried under vacuum at 50 °C for 6 hours to obtain the precursor Bi@Ce-UiO-66-Br. The other steps were the same as in Example 1, resulting in a Ce-UiO-66-Br-coated Bi metal core-shell catalyst. Based on the total mass of the obtained catalyst, the mass percentage of metallic Bi was 30%, denoted as 30BiNPs@CUB.

[0037] Example 4

[0038] In step 2 of this embodiment, 72.8 mg (0.15 mmol) of bismuth nitrate pentahydrate was ultrasonically dissolved in 25 mL of acetone, and 100 mg of Ce-UiO-66-Br was added. The mixture was stirred at room temperature for 12 hours, centrifuged, and the solid was washed three times with anhydrous ethanol and then dried under vacuum at 50°C for 6 hours to obtain the precursor Bi@Ce-UiO-66-Br. The other steps were the same as in Example 1, resulting in a Ce-UiO-66-Br-coated Bi metal core-shell catalyst. Based on the total mass of the obtained catalyst, the mass percentage of metallic Bi was 25%, denoted as 25BiNPs@CUB.

[0039] Comparative Example 1

[0040] 121.3 mg (0.25 mmol) of bismuth nitrate pentahydrate was dissolved in 25 mL of acetone by sonication. After stirring for 15 minutes, 100 mg (2.64 mmol) of sodium borohydride was added, and the mixture was stirred at room temperature for 10 minutes. The mixture was then centrifuged, and the solid was washed with anhydrous methanol (10 mL × 3 times) and anhydrous ethanol (10 mL × 3 times) to remove excess sodium borohydride and byproducts, yielding the Bi metal catalyst, denoted as BiNPs.

[0041] Comparative Example 2

[0042] In step 2 of this embodiment, 169.8 mg (0.35 mmol) of bismuth nitrate pentahydrate was ultrasonically dissolved in 25 mL of acetone, and 100 mg of Ce-UiO-66-Br was added. The mixture was stirred at room temperature for 12 hours, centrifuged, and the solid was washed three times with anhydrous ethanol and then dried under vacuum at 50°C for 6 hours to obtain the precursor Bi@Ce-UiO-66-Br. The other steps were the same as in Example 1, resulting in a Ce-UiO-66-Br-coated Bi metal core-shell catalyst. Based on the total mass of the obtained catalyst, the mass percentage of metallic Bi was 45%, denoted as 45BiNPs@CUB.

[0043] The catalysts prepared in the above examples and comparative examples were characterized in terms of structure and morphology, and the results are shown in Figures 1-3. As can be seen from Figure 1, the diffraction peaks of Ce-UiO-66-Br prepared in Example 1 are consistent with the standard UiO-66 structure reported in the literature, indicating that the MOF support is well crystallized. The BiNPs@CUB prepared in Examples 1-3 not only retained the characteristic peaks of the support, but also showed obvious diffraction peaks at 27.2°, 38.0°, 39.6°, 48.7° and 56.0°, which correspond to the (012), (104), (110), (202) and (024) crystal planes of BiNPs prepared in Comparative Example 1 (refer to standard card JCPDS 44-1246). As can be seen from the Fourier transform infrared spectrum in Figure 2, Ce-UiO-66-Br prepared in Example 1 exhibits typical Ce-UiO-66 structural characteristic peaks. Among them, the peak at 1580 cm⁻¹ is particularly prominent. -1 The nearby absorption peak is attributed to the asymmetric stretching vibration (CO) of the carboxyl group, 1385 cm⁻¹. -1 The nearby peaks are attributed to the symmetric stretching vibration (COO-) of the carboxyl group, while the peak at 765 cm⁻¹ is... -1 The nearby peaks correspond to the vibrations of the Ce-O bond. The characteristic peaks of the Ce-UiO-66 framework in the BiNPs@CUB prepared in Examples 1-3 were all retained, proving that the Ce-UiO-66 support remained chemically stable after composite formation. The SEM and TEM results in Figure 3 show that the Ce-UiO-66-Br prepared in Example 1 exhibits a regular octahedral morphology, while the surface of the 35BiNPs@CUB prepared in Example 1 is rougher. HRTEM images show that the shell thickness of Ce-UiO-66-Br is approximately 5.84 nm, and the 0.33 nm lattice fringes measured in the Bi metal core correspond to the (012) crystal plane of BiNPs. The distribution range of C, Ce, Br, and Bi elements in the composite material in the EDSMapping diagram proves that Ce-UiO-66-Br successfully coats Bi metal.

[0044] Example 5

[0045] Applications of the catalysts prepared in Examples 1-4 for photocatalytic reduction of CO2 to CH4

[0046] 0.015 g of catalyst was weighed and added to 3 mL of anhydrous ethanol. The mixture was sonicated for 1 minute to ensure uniform dispersion. The dispersed catalyst was then spin-coated evenly onto a 6 cm diameter petri dish. After drying at 60 °C, the petri dish was placed in a 500 mL transparent, sealed reactor. 50 μL of deionized water was added. No co-catalysts or sacrificial agents were added. High-purity CO2 was introduced into the reactor, and the reaction was simulated by a 300 W xenon lamp for 2 hours. Changes in the reactant gases were detected using gas chromatography. Comparative experiments were conducted using catalysts prepared in Examples 1 and 2 and Ce-UiO-66-Br. The results are shown in Figures 4 and 5.

[0047] As shown in Figure 4, the catalysts prepared in Examples 1-4 exhibited high CO2 reduction activity and CH4 selectivity when used in the photocatalytic CO2 reduction reaction. Among them, the 35BiNP@CUB prepared in Example 1 showed the best reduction performance, with CH4 and CO production of 57.75 μmol·g⁻¹ after 2 hours of reaction. -1 and 34.38 μmol·g -1 The CH4 selectivity of the product reached 87.04%. As shown in Figure 5, the effective photogenerated electron rate of the catalysts prepared in Examples 1-4 for the photocatalytic CO2 reduction reaction was significantly higher than that of the catalysts in Comparative Example 1 and Comparative Example 2. Moreover, the effective photogenerated electron rate of the 35BiNPs@CUB catalyst prepared in Example 1 after 2 hours of irradiation was 530.76 μmol·g. -1 It is 2.46 times that of Ce-UiO-66-Br.

[0048] The catalysts prepared in Examples 1-4 and Comparative Example 2 were used to reduce CO2 according to the above method. After the reaction was complete, they were recycled twice in the same way, and their recycling performance was tested. The results are shown in Figures 6 and 7. As can be seen from the figures, after three cycles, the catalysts prepared in Examples 1-4 still have good reduction stability. This is attributed to the tight bonding between Ce-UiO-66-Br and Bi metal in the core-shell catalyst.

[0049] The structure of 35BiNP@CUB prepared in Example 1 after three cycles was further characterized, and the results are shown in Figure 8. As can be seen from the figure, the characteristic peaks of the 35BiNP@CUB crystal structure did not change significantly before and after the reaction, indicating that the crystal structure of 35BiNP@CUB did not change during the reaction.

[0050] To investigate the effect of Br-based ligand functionalization on the adsorption capacity of Ce-UiO-66 for CO2 and CH4 in the catalyst of this invention, the adsorption energy of Ce-UiO-66 with different ligand functionalizations was calculated using density functional theory (DFT), and the results are shown in Figure 9. As can be seen from the figure, Ce-UiO-66-Br exhibits the best CO2 adsorption capacity and the lowest CH4 adsorption capacity. Therefore, using Br-based ligand-functionalized Ce-UiO-66 to encapsulate Bi metal can efficiently adsorb CO2 for subsequent photocatalytic reactions, and the generated CH4 can be rapidly desorbed, thereby precisely controlling the CO2 reduction pathway to directionally generate CH4.

Claims

1. A Bi@Ce-UiO-66-Br catalyst, characterized in that: The catalyst consists of a metallic Bi core and a Ce-UiO-66 shell, functionalized with Br-group ligands, encapsulating the metallic Bi core; wherein, based on the total mass of the catalyst, the mass percentage of metallic Bi is 25%–40%; the catalyst is prepared by the following method: Step 1: 2-bromoterephthalic acid is dissolved in N,N-dimethylformamide, and cerium ammonium nitrate is dissolved in deionized water, then the two solutions are mixed at 80–120 °C. The reaction was stirred at °C for 20–60 minutes. After the reaction, the solid was washed with N,N-dimethylformamide and acetone in sequence, and dried to obtain Br-ligand-functionalized Ce-UiO-66. Step 2: Bismuth nitrate was sonicated and dissolved in acetone, and Br-ligand-functionalized Ce-UiO-66 was added. The mixture was stirred at room temperature for 8–12 hours, centrifuged, and the solid was washed with anhydrous ethanol and dried under vacuum to obtain the precursor Bi@Ce-UiO-66-Br. Step 3: The precursor Bi@Ce-UiO-66-Br was added to ethanol, stirred evenly, and sodium borohydride was added. The mixture was stirred at room temperature for 5–30 minutes, centrifuged, and the solid was washed with anhydrous methanol and anhydrous ethanol in sequence to obtain the catalyst.

2. The Bi@Ce-UiO-66-Br catalyst according to claim 1, characterized in that: Based on the total mass of the catalyst, the mass percentage of metallic Bi is 35%.

3. The Bi@Ce-UiO-66-Br catalyst according to claim 1, characterized in that: In step 1, the molar ratio of 2-bromoterephthalic acid and cerium ammonium nitrate is 1:1.4 to 1:1.

6.

4. The Bi@Ce-UiO-66-Br catalyst according to claim 1, characterized in that: In step 1, the volume ratio of deionized water to N,N-dimethylformamide is 1:3 to 1:

4.

5. The Bi@Ce-UiO-66-Br catalyst according to claim 1, characterized in that: In step 1, stir the reaction at 100°C for 30–40 minutes.

6. The Bi@Ce-UiO-66-Br catalyst according to claim 1, characterized in that: In step 3, the amount of sodium borohydride added is 8 to 13 times the molar amount of Bi in the precursor Bi@Ce-UiO-66-Br.

7. Use of the Bi@Ce-UiO-66-Br catalyst according to any one of claims 1 to 6 for photocatalytic reduction of CO2 to CH4.

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