Efficient CO2 Utilization Research Articles

(Invited) Preparation of Aucu Alloy Nanoparticles Via Ionic Liquid/Metal Sputtering for Electrocatalytic CO2 Reduction

Development of highly active electrocatalysts for carbon dioxide reduction has been intensively investigated for the efficient utilization of CO2 and the lowering of electric energy consumption. Among various strategies, alloy nanoparticles (NPs) have attracted significant interest due to their tunable catalytic properties, which can be adjusted by altering their chemical composition and particle size. Recently, we reported novel preparation methods of metal nanoparticles through the sputter deposition of metals onto room-temperature ionic liquids (RTILs), a technique we termed “RTIL/metal sputtering technique”. This method enabled the formation of metal and alloy NPs, such as Au, Ag, Pd, Pt, AuAg, AuCu, AuPt and AuRh,(1-6) with sizes in the nanometer ranges, in the absence of additional stabilizing agents. Here we report the preparation of AuCu alloy NPs via RTIL/metal sputtering and evaluate their electrocatalytic activity for CO2 reduction as a function of the alloy composition.The simultaneous sputtering of Au and Cu onto RTILs produced AuCu alloy NPs with the size ranging from 3 to 4 nm. Subsequent loading of these sputter-deposited AuCu NPs in RTIL on carbon black powders (CB) not only increased the AuCu NP size to 3-7 nm but also facilitated alloying between Au and Cu. The chemical composition of AuCu NPs was controlled by changing the area fraction of Au plates in Au-Cu binary targets used for sputtering. The XRD analysis revealed that thus-obtained AuCu NPs had the fcc structure, in which each peak shifted to a lower angle with an increase in the Au fraction.The prepared AuCu/CB powers were immobilized on glassy carbon electrodes and used for the electrocatalyst for CO2 reduction in a 0.5 M KHCO3 aqueous solution. Cyclic voltammetry revealed that cathodic currents were observed at potentials more negative than -1.2 V, with the current intensity being higher under a CO2 atmosphere compared to an N2 atmosphere. This confirms the CO2 reduction activity of AuCu nanoparticles. Constant potential electrolysis was carried out at -2 V vs. Ag/AgCl in a CO2 atmosphere. As CO2 reduction products, CO and HCOOH were formed. The selectivity of these products was remarkably influenced by the composition of AuCu alloy NPs: The HCOOH selectivity increased with a higher Cu ratio, while the CO selectivity showed a volcano-type relationship, reaching an optimum at the Au fraction in NPs of ca. 0.8. H2 was also produced as a byproduct, with its selectivity being minimized at the Au fraction of 0.6-0.9. In conclusion we demonstrated the importance of alloy composition in optimizing the electrocatalytic performance of AuCu NPs for CO2 reduction. References T. Torimoto, et al., Appl. Phys. Lett. 89, 243117 (2006) .K. Okazaki, et al, Chem. Commun. 691-693 (2008) .M. Hirano, et al., Chem. Chem. Phys. 15, 7286-7294 (2013).S. Suzuki, et al., 44, 4186-4194, (2015).S. Suzuki, et al., CrystEngComm, 14, 4922-4926 (2012)K. Akiyoshi, et. al, Phys. Chem. Chem. Phys., 24, 24335 (2022) .

Cascade Catalytic Systems for Converting CO2 into C2+ Products.

The excessive emission and continuous accumulation of CO2 have precipitated serious social and environmental issues. However, CO2 can also serve as an abundant, inexpensive, and non-toxic renewable C1 carbon source for synthetic reactions. To achieve carbon neutrality and recycling, it is crucial to convert CO2 into value-added products through chemical pathways. Multi-carbon (C2+) products, compared to C1 products, offer a broader range of applications and higher economic returns. Despite this, converting CO2 into C2+ products is difficult due to its stability and the high energy required for C-C coupling. Cascade catalytic reactions offer a solution by coordinating active components, promoting intermediate transfers, and facilitating further transformations. This method lowers energy consumption. Recent advancements in cascade catalytic systems have allowed for significant progress in synthesizing C2+ products from CO2. This review highlights the features and advantages of cascade catalysis strategies, explores the synergistic effects among active sites, and examines the mechanisms within these systems. It also outlines future prospects for CO2 cascade catalytic synthesis, offering a framework for efficient CO2 utilization and the development of next-generation catalytic systems.

Efficient paddle-wheel copper cluster-based metal-organic framework for catalytic conversion of CO2 to oxazolidinones under mild conditions

Efficient utilization of CO2 and its conversion into high-value-added products contribute to mitigating environmental issues such as the greenhouse effect. Among these methods, the carboxylation cyclization of CO2 with propargylic amine represents a green and atom-economical approach. Developing cost-effective catalyst that can promote this reaction under mild condition is desirable but challenging. Herein, a unique two-dimensional (2D) metal–organic framework (MOF) {[Cu(QCA)2]∙0.5DMF∙0.5H2O}n (1) (QCA =6-quinolinecarboxylic acid, DMF = N,N-dimethylformamide) have been synthesized and thoroughly characterized. Compound 1 was constructed from paddle-wheel dinuclear copper clusters [Cu2(COO)4] and carboxylate ligands, presenting a two-dimensional framework with new topology. Stability tests indicate that compound 1 undergoes reversible structural changes in different solvents and exhibits good thermal stability. 1 as heterogeneous catalyst enabled the transformation of CO2 and propargylic amine into oxazolidinones under mild conditions with broad substrate generality. In addition, 1 could maintain its catalytic performance with five continuous reactions. This work presents an infrequent example of a 2D noble metal free MOF-based catalyst that shows high catalytic efficiency under mild conditions.

ZIF-8 Porous Liquids with Different Sterically Hindered Solvents and Porous Guests for Catalytic Conversion of Carbon Dioxide.

Utilizing carbon dioxide (CO2) as a raw material is an effective way to reduce carbon emissions, and developing catalytic systems with high catalytic activity and stability is crucial for the efficient utilization of CO2. Porous liquids (PLs) with both permanent pores and fluidity have great potential in the fields of catalysis, gas sorption, and storage. Nevertheless, the catalytic performance of PLs is affected by many factors; therefore, further study is needed. Herein, we proposed a general strategy to construct a series of type III PLs with different chemical structures of sterically hindered solvents and different microstructures of porous guests. Benefiting from the unique microstructures, the as-prepared PLs exhibit great potential in catalyzing the reaction of CO2 with propylene oxide under suitable conditions. Moreover, their catalytic activity exceeds that of pure sterically hindered solvents without a porous guest loading. The influences of the nucleophilicity of the anion of the sterically hindered solvent and the microstructure of the porous guests on the catalytic activity and the catalytic stability of the PLs were analyzed. Meanwhile, the mechanism of the catalytic conversion of CO2 was proposed, which is of great significance for the design and development of the subsequent PL catalysts.

Tandem Pt/TiO2 and Fe3C catalysts for direct transformation of CO2 to light hydrocarbons under high space velocity

CO2 hydrogenation to hydrocarbons under high space velocity is crucial for industrial applications, but traditional Fe-based catalysts often suffer from the low activity and poor stability. Herein, we report a new tandem catalyst system combining Pt/TiO2 catalysts with Fe3C catalysts for the direct conversion of CO2 into C2-C4 hydrocarbons under high space velocity. The Pt/TiO2 component promotes *CO intermediate production with an enhanced Reverse Water-Gas Shift (RWGS) reaction efficiency, providing a highly reactive species for the Fe3C catalyst to achieve Fischer-Tropsch synthesis (FTS). By maximizing the contact interface between the Pt/TiO2 and Fe-based components through a granule mixing configuration, we achieve significant enhancements in both CO2 conversion rate (24.0 %) and C2-C4 hydrocarbons selectivity (51.1 %) under the gaseous hourly space velocity (GHSV) of 100000 mL gcat−1h−1. Besides, excellent stability is achieved by the tandem catalysts with continuous catalysis for up to 80 h without significant decrease in activity. Through modulation of the reduction states of iron oxide, we effectively tune the composition of Fe-based catalyst, thereby tailoring the product distribution. Through this work, we not only offer a promising avenue for reducing CO2 for efficient CO2 utilization but also highlight the importance of catalyst design in advancing sustainable chemical synthesis.

Redesigning glycolaldehyde synthase for the synthesis of biorefinery feedstock D-xylulose from C1 compounds.

Global climate deterioration intensifies the demand for exploiting efficient CO2 utilization approaches. Converting CO2 to biorefinery feedstock affords an alternative strategy for third-generation biorefineries. However, upcycling CO2 into complex chiral carbohydrates remains a major challenge. Previous attempts at sugar synthesis from CO2 either produce mixtures with poor stereoselectivity or require ATP as a cofactor. Here, by redesigning glycolaldehyde synthase, the authors constructed a synthetic pathway for biorefinery feedstock D-xylulose from CO2 that does not require ATP as a cofactor. The artificial D-xylulose pathway only requires a three-step enzyme cascade reaction to achieve the stereoselective synthesis of D-xylulose at a concentration of 1.2gL-1. Our research opens up an alternative route toward future production of chemicals and fuels from CO2.

Quaternarized chitosan nanofiber and ZIF aerogel composites for synergetic CO2 cycloaddition catalysis

Chemical upcycling of CO2, a major greenhouse gas, is attracting significant attention as a crucial strategy to combat global warming. The production of cyclic carbonate using metal-organic frameworks and their composites using nanofibrous carbohydrate polymer are promising ways to convert CO2 into valuable products. However, the current role of fibrous polymers is restricted to serving as physical substrates. This study seeks to expand the functionality of quaternarized chitosan nanofibers into synergistic catalysts in addition to their physical support role. A novel aerogel composite using Co/Zn-ZIF catalyst and quaternarized chitosan nanofiber (Q-CsNF+) was fabricated, and its hierarchical pore structure was extensively discussed. The obtained ZIF/Q-CsNF+ composite can synergistically convert epoxide to cyclic carbonate by acting as a co-catalyst. Moreover, we determined the predominant factors influencing catalytic activity in CO2 cycloaddition, especially by examining the interplay between CO2 affinity and co-catalyst effects. This research provides fundamental insight into developing CO2 cycloaddition catalysts using nature-derived fibrous polymers, opening new avenues for sustainable and efficient CO2 utilization.

Advancements in covalent organic framework‐based nanocomposites: Pioneering materials for CO2 reduction and storage

AbstractThe persistent increase in atmospheric carbon dioxide (CO2) concentration poses a significant contemporary challenge. Contemporary chemistry is heavily focused on sustainable solutions, particularly the photo‐/electrocatalytic reduction of CO2 and its utilization for energy storage. Despite promising prospects, efficient chemical CO2 conversion faces obstacles such as ineffective CO2 uptake/activation and catalyst mass transport. Covalent organic frameworks (COFs) have emerged as potential catalysts due to their precise structural design, functionalizable chemical environments, and robust architectures. COF‐based materials, especially those incorporating diverse active sites like single metal sites, metal nanoparticles, and metal oxides, hold promise for CO2 conversion and energy storage. This review sheds light on CO2 photoreduction/electroreduction and storage in Li‐CO2 batteries catalyzed by COF‐based composites, focusing on recent advancements in integrating COFs with nanoparticles for CO2 reduction. It discusses design principles, synthesis methods, and catalytic mechanisms driving the enhanced performance of COF‐based nanocomposites across various applications, including electrochemical reduction, photocatalysis, and lithium CO2 batteries. The review also addresses challenges and prospects of COF‐based catalysts for efficient CO2 utilization, aiming to steer the development of innovative COF‐based nanocomposites, thus advancing sustainable energy technologies and environmental stewardship. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

Continuous CO2 capture and reduction to CO by circulating transition-metal-free dual-function material in fluidized-bed reactors

To mitigate global warming and achieve a sustainable society, innovative technologies for efficient CO2 utilization are required. Integrated CO2 capture and reduction (CCR) using dual-function materials (DFMs) is favorable owing to its potentially low energy consumption, capital investment, and processing costs. Although numerous studies have focused on catalytic science, continuous and steady-state CCR operations have not been sufficiently addressed from an engineering perspective. In this study, a circulating fluidized bed (CFB) system is investigated for continuous CCR to syngas (CO + H2). In the CFB system, transition-metal-free DFM (Na/Al2O3) particles are circulated between two bubbling fluidized-bed reactors. The DFM captures CO2 in one reactor (CO2 capture reactor) and reduces the captured CO2 to CO by the reaction with H2 in the other reactor (H2 reactor). The effluent gas concentrations from both reactors reach steady state and are maintained for over 8 h. For the product gas from the H2 reactor, the CO2 conversion and CO selectivity exceed 80 % and 99 %, respectively. However, the H2 conversion is <20 %, indicating a potential challenge for the CFB system for integrated CCR. Furthermore, this study confirms that the H2/CO ratio for syngas can be controlled by adjusting the experimental conditions (particularly, the H2 flow rate). Consequently, the CFB system can be modified to facilitate the interaction between H2 gas and the DFM particles.

Ag–Cr2O3 interfaces with local alkaline microenvironments for electroreduction of CO2 to CO in an acidic electrolyte

Electrochemical CO2 reduction in acidic electrolyte is a potential strategy for efficient CO2 utilization by preventing the formation of carbonate, but it remains a great challenge to improve the selectivity of CO2 reduction in acidic electrolytes due to the competitive hydrogen evolution reaction. Herein, we demonstrate Ag2CrO4 derived Ag–Cr2O3 composite catalyst with local alkaline microenvironments for enhanced selectivity of CO2 to CO product in an acidic KCl electrolyte. Under the electrochemical reduction of CO2, the Ag2CrO4 pre-catalyst undergoes a chemical transformation induced by chloride ions to generate AgCl–Cr2O3, meanwhile, AgCl is electrochemically reduced Ag to form a Cr2O3 coated Ag composite catalyst with rich Ag–Cr2O3 interfaces. The Ag–Cr2O3 gas diffusion electrode constructed from carbon nanopowder effectively increases the hydrophobicity of the electrode, and the optimized electrode exhibits high CO Faradaic efficiency (FE) (over 75%) at a wide current density of 50–300 mA cm-2 and achieves a maximum FE of 86.7% toward CO product at 300 mA cm-2. The in situ Raman spectroscopy reveals that Cr2O3 can adsorb OH− which regulates the local alkaline environment to promote the CO2 adsorption on the Ag–Cr2O3 interface and stabilize the *CO2-/*COOH intermediates in the acidic electrolyte. This work provides an effective strategy to tune the reaction interfaces for CO2 reduction in acidic electrolytes.

The Heptazine-Based Materials through Intrinsically Modification for the Cycloaddition of CO2 and Bisepoxides.

For the efficient utilization of CO2 into valuable product, the attractive carbon nitride catalysts have been widely studied. In this work, heptazine-related materials with varying degree of polymerization were designed by an intrinsically modification strategy and employed in the cycloaddition of CO2 with the bisepoxide 1, 4-butanediol diglycidyl ether (BDODGE). We initially figured out that the sample prepared at 450 °C contained more melem hydrate, exhibiting the best performance. The epoxides conversion and corresponding cyclic carbonates selectivity could achieve 93.1 % and 99.3 % at 140 °C for 20 h without any cocatalyst and solvent, respectively. Results of the catalytic tests suggested that the high catalytic activity was dependent on big size porous structure and the synergetic effect of active amino groups and -OH groups. The role of water in maintaining the specific structure and providing active site has been proved. Moreover, the CN-450-W catalyst exhibited outstanding recycling stability. And finally, a plausible reaction mechanism was proposed.

Deciphering the structural evolution and real active ingredients of iron oxides in photocatalytic CO2 hydrogenation

Photocatalytic CO2 hydrogenation reactions can produce high-value-added chemicals for industry, solving the environmental problems caused by excessive CO2 emissions. Iron oxides are commonly used in photocatalytic reactions due to their various structures and suitable band gaps. Nevertheless, the structural evolution and real active components during photocatalytic CO2 hydrogenation reaction are rarely studied. Herein, a variety of iron oxides including α-Fe2O3, γ-Fe2O3, Fe3O4 and FeO were derived from Prussian blue precursors to investigate the CO2 hydrogenation performance, structural evolution and active components. Especially, the typical α- and γ-Fe2O3 are converted to Fe3O4 during the reaction, while Fe/FexOy remains structurally stable. Meanwhile, it is confirmed that Fe3O4 is the main active component for CO production and the formation of hydrocarbons (CH4 and C2–C4) are highly dependent on the Fe/FexOy heterojunctions. The optimal yields of CO, CH4 and C2–C4 hydrocarbons over the best catalyst (FeFe-550) can achieve 4 mmol g−1 h−1, 350 μmol g−1 h−1 and 150 μmol g−1 h−1, respectively due to their suitable metal/oxide component distribution. This work examines the structural evolution of different iron oxide catalysts in the photocatalytic CO2 hydrogenation reaction, identifies the active components as well as reveals the relationship between components and the products, and offers valuable insights into the efficient utilization of CO2.

Sulfidation-Induced Surface Local Electronic and Atomic Structures in a Silver Catalyst Enables Silicon Photocathode for Selective and Efficient Photoelectrochemical CO2 Reduction.

Converting CO2 to value-added chemicals through a photoelectrochemical (PEC) system is a creative approach toward renewable energy utilization and storage. However, the rational design of appropriate catalysts while being effectively integrated with semiconductor photoelectrodes remains a considerable challenge for achieving single-carbon products with high efficiency. Herein, we demonstrate a novel sulfidation-induced strategy for in situ grown sulfide-derived Ag nanowires on a Si photocathode (denoted as SD-Ag/Si) based on the standard crystalline Si solar cells. Such an exquisite design of the SD-Ag/Si photocathode not only provides a large electrochemically active surface area but also endows abundant active sites of Ag2S/Ag interfaces and high-index Ag facets for PEC CO production. The optimized SD-Ag/Si photocathode displays an ideal CO Faradic efficiency of 95.2% and an onset potential of +0.26 V versus the reversible hydrogen electrode, ascribed to the sulfidation-induced synergistic effect of the surface atomic arrangement and electronic structure in Ag catalysts that promote charge transfer, facilitate CO2 adsorption and activation, and suppress hydrogen evolution reaction. This sulfidation-induced strategy represents a scalable approach for designing high-performance catalysts for electrochemical and PEC devices with efficient CO2 utilization.

Enhancing Efficiency and High-Value Chemicals Generation through Coupling Photocatalytic CO2 Reduction with Propane Oxidation.

Conversion of CO2 into high-value chemicals using solar energy is one of promising approaches to achieve carbon neutrality. However, the oxidation of water in the photocatalytic CO2 reduction is kinetically unfavorable due to multi-electron and proton transfer processes, along with the difficulty in generating O-O bonds. To tackle these challenges, this study investigated the coupling reaction of photocatalytic CO2 reduction and selective propane oxidation using the Pd/P25 (1 wt%) catalyst. Our findings reveal a significant improvement in CO2 reduction, nearly fivefold higher, achieved by substituting water oxidation with selective propane oxidation. This substitution not only accelerates the process of CO2 reduction but also yields valuable propylene. The relative ease of propane oxidation, compared to water, appears to increase the density of photogenerated electrons, ultimately enhancing the efficiency of CO2 reduction. We further found that hydroxyl radicals and reduced intermediate (carboxylate species) played important roles in the photocatalytic reaction. These findings not only propose a potential approach for the efficient utilization of CO2 through the coupling of selective propane oxidation into propylene, but also provide insights into the mechanistic understanding of the coupling reaction.

CO2 Hydrogenation to Hydrocarbons over Fe‐Based Catalysts: Status and Recent Developments

AbstractTo control anthropogenic CO2 emissions worldwide, it is necessary not only to align the chemical industry and energy sector with renewable resources but also to implement large‐scale utilization of CO2 as a feedstock. The Fe‐catalyzed CO2‐modified Fischer‐Tropsch Synthesis (CO2‐FTS) is one of the most promising options for efficient CO2 utilization, as it can be used to synthesize desired higher hydrocarbons (C2+), including lower olefins (C2=‐C4=), the main building blocks of the chemical industry, and long‐chain hydrocarbons (C5+), which can be used as fuels. To optimize catalyst and process design for the purpose of developing an economically viable industrial process, the reaction mechanism and the factors controlling product selectivity need to be fully understood. This article discusses the current state‐of‐the‐art in catalyst design and approaches for making effective progress in addressing these challenges.

Recent Advances in Hydrogenation of CO2 to CO with Heterogeneous Catalysts Through the RWGS Reaction.

With the continuous increase in CO2 emissions, primarily from the combustion of coal and oil, the ecosystem faces a significant threat. Therefore, as an effective method to minimize the issue, the Reverse Water Gas Shift (RWGS) reaction which converts CO2 towards CO attracts much attention, is an environmentally-friendly method to mitigate climate change and lessen dependence on fossil fuels. Nevertheless, the inherent thermodynamic stability and kinetic inertness of CO2 is a big challenge under mild conditions. In addition, it remains another fundamental challenge in RWGS reaction owing to CO selectivity issue caused by CO2 further hydrogenation towards CH4 . Up till now, a series of catalysis systems have been developed for CO2 reduction reaction to produce CO. Herein, the research progress of the well-performed heterogeneous catalysts for the RWGS reaction were summarized, including the catalyst design, catalytic performance and reaction mechanism. This review will provide insights into efficient utilization of CO2 and promote the development of RWGS reaction.

Investigation of intermediates formation in the CO2 hydrogenation to methanol reaction over Ni5Ga3-ZrO2-SBA-15 materials prepared via ZrO2 atomic layer deposition

The production of methanol through CO2 hydrogenation holds great promise for efficient CO2 utilization. The development of catalysts that exclusively favor the formate route is desirable as this enhances methanol selectivity and avoids CO formation. Here, the synthesis of two groups of Ni5Ga3-ZrO2-SBA-15 based materials was studied through the atomic layer deposition (ALD) of ZrO2. The first group was prepared applying ZrO2 ALD over a Ni5Ga3/SBA-15 material and the second group was prepared doing ZrO2 ALD over a mesoporous silica, Santa Barbara Amorphous (SBA-15), followed by impregnation with Ni5Ga3. Some characterization techniques were employed to assess the effectiveness of the ZrO2 ALD on both groups. Interestingly, it was observed that ZrO2 deposition was less effective over the Ni5Ga3/SBA-15 sample compared to its deposition over pure SBA-15, and through XPS analysis was noticed that ZrO2 is probably covering part of the Ni5Ga3 alloys. Furthermore, in situ DRIFTS analysis was performed during reaction conditions and revealed that ZrO2 deposition facilitated the formation of formate and methoxy intermediates in both material groups. The increase in the ZrO2 ALD cycles increased the formate and methoxy bands and decreased CO-related bands. After 6 cycles, only the ZrSBANG_6 catalyst exclusively followed the formate route, as only formate and methoxy bands were present.

Towards understanding the reaction network in the hydrogenation of CO2-derived ethylene carbonate

The selective hydrogenation of ethylene carbonate (EC) to produce methanol (MeOH) and ethylene glycol (EG) is a crucial route to achieve indirect and efficient utilization of CO2 under mild reaction conditions. Nonetheless, due to the cyclic carbonate structure of EC, the intricate reaction network involved in the hydrogenation process has not been systematically reported yet. Here, a series of Cu/SiO2 catalysts were designed to investigate the related reaction pathways. The catalytic evaluation results, coupled with thermodynamic calculations, reveal that there are several competitive side-reactions other than EC hydrogenation to MeOH and EG, including decarboxylation, hydrolysis and decarbonylation reactions to produce CO2 and CO as byproducts. Moreover, the distribution of products is significantly influenced by evaluation conditions. Furthermore, by doping metal oxides to adjust the surface properties of Cu/SiO2 catalyst, it is found that acidic sites could promote EC hydrolysis, whereas basic sites predominantly facilitate EC decarboxylation and decarbonylation reactions. Overall, a comprehensive reaction network of EC hydrogenation is systematically proposed to provide appropriate evaluation conditions and guidance for designing new catalysts to minimize unwanted side reactions, which is of great significance to enhance the indirect utilization of CO2.

Boosting catalytic performance for CO2 cycloaddition under mild condition via amine grafting on MIL-101-SO3H catalyst

The efforts to achieve sustainable chemical conversion and efficient CO2 utilization are critical to addressing climate change and environmental sustainability, and therefore the development of effective CO2 conversion catalysts is crucial. In this study, novel acid-base bifunctional catalysts, MIL-101-SO3H@Atz and MIL-101-SO3H@DAtz, were successfully synthesized using MIL-101-SO3H as an acid support material through post-synthetic modification with 3-amino-1,2,4-triazole (Atz) and 3,5-diamino-1,2,4-triazole (DAtz) for CO2 conversion reaction. The incorporation of the amine species into MIL-101-SO3H created unique synergistic effects with dual acid-base catalytic sites, facilitating the efficient conversion of CO2 and epoxides into cyclic carbonates. Among the catalysts, MIL-101- SO3H@DAtz demonstrated superior catalytic performance with achieving 100% epichlorohydrin (ECH) conversion with over 99% selectivity to cyclic carbonate with high selectivity of > 99% under the ambient condition of 1 bar CO2 without any co-catalyst or solvent. The elucidated CO2 cycloaddition reaction mechanism highlights the synergistic effects of acid-base functionalities and CO2-philic Lewis bases as well as hydrogen bonding donor groups, providing valuable insights into the factors contributing to superior catalytic performance. The simulated flue gas (15% CO2/85% N2, v/v) was also conducted using MIL-101-SO3H@DAtz catalyst. Additionally, the MIL-101-SO3H@DAtz catalyst exhibited remarkably robust structural stability and recyclability, maintaining its activity over multiple cycles.

Modulation of Fe–MOF via second-transition metal ion doping (Ti, Mn, Zn, Cu) for efficient visible-light driven CO2 reduction to CH4

This study developed metal–organic frameworks (MOFs) with enhanced properties for CO2 conversion by doping second- transition metal ions (Ti, Mn, Zn, and Cu) into Fe–MOF, which resulted in Fe-M−MOF (M = Ti, Mn, Zn, or Cu). The selection of different metal species in the metal cluster nodes of the MOFs significantly impacted the CO2 conversion efficiency. Among the different combinations, the Fe–Cu bimetallic cluster node was identified as the most optimal node. In addition, we investigated various variables and preparation conditions for determining the optimal synthesis conditions for Fe–Cu-MOFs. We observed that a synthesis temperature, time, and pH of 130 °C, 15 h, and 3.2, respectively, yielded the best results. The 13CO2 isotope labeling method confirmed that the carbon source of CO and CH4 were derived from CO2. Under simulated visible-light irradiation (λ ≥ 420 nm), Fe–Cu-T130 exhibited the highest photocatalytic activity, with a CH4 generation rate of up to 444.2 μmol g−1 h−1. This high activity was attributed to several factors. First, the presence of Fe2+, Fe3+, and Cu2+ on the surface of Fe–Cu-T130 resulted in photogenerated electrons and holes under visible-light excitation. Fe2+ accepted electrons to reduce CO2, whereas Fe3+ and Cu2+ oxidized H2O through holes. Second, the polycrystalline structure of Fe–Cu-T130 with abundant surface oxygen vacancies enhanced the chemical reactivity. Finally, the low conduction band position and narrower bandgap of Fe–Cu-T130 facilitated the excitation of electrons into the conduction band, thereby promoting the CO2 reduction reaction. This study successfully demonstrated the enhanced photocatalytic activity of Fe–Cu-T130 for CO2 conversion under visible light. The findings provide insight into the development of MOFs with improved properties for the sustainable and efficient utilization of CO2.