Efficient Conversion Of CO2 Research Articles

Construction of dual vacancies and frustrated Lewis Pairs-modified Bi2WO6 nanosheets for efficient photocatalytic conversion of CO2 to CO

Surface vacancy engineering is an attractive modification strategy for constructing efficient photocatalysts. However, the monovacancy-modified photocatalysts exhibit limited activity in the CO2 reduction reaction (CO2RR), primarily due to their low efficiency in separating electron-hole pairs and weak CO2 binding affinity. Herein, a photocatalyst (In2O3-x(OH)y/Bi2WO6-VBi,O) was developed, consisting of Bi/O vacancies-rich Bi2WO6 (Bi2WO6-VBi,O) and In2O3-x(OH)y modified by surface frustrated Lewis pairs (SFLPs). Bi vacancies (VBi) and O vacancies (VO) are categorized as cationic and anionic vacancies, respectively. In comparison to monovacancy-modified photocatalysts, the above photocatalyst can bind the O and C atoms of CO2 to VBi and VO in a bidentate-bonding mode, as opposed to a monodentate-bonding mode, thus achieving robust adsorption and rapid activation of CO2 molecules. The findings from the molecular simulation suggest that dual vacancies and SFLPs enhance CO selectivity by accelerating the desorption step of the intermediate product *CO to CO. Moreover, the directional transfer of electrons from VO to VBi favors the separation of electron-hole pairs. The optimal sample (4.3 %In2O3-x(OH)y/Bi2WO6-VBi,O) has an excellent CO production rate of 191.8 μmol·gcat-1·h−1, 6.6 times that of Bi2WO6, and superior CO selectivity around 100 %. By manipulating dual vacancies and SFLPs, this research contributes to developing novel photocatalysts and elucidates the underlying mechanism of CO2 photoreduction.

Solar Energy-Driven Reverse Water Gas Shift Reaction: Photothermal Effect, Photoelectric Activation and Selectivity Regulation.

Excessive carbon dioxide (CO2) emissions are one of the main causes of the greenhouse effect. Thermal catalytic reverse water gas shift (RWGS) reaction, which is a pre reaction for Fischer-Tropsch synthesis, is considered an effective way to convert CO2 and synthesize high value-added chemicals in industry. However, traditional thermal catalysis requires a large amount of fossil fuels to drive reactions, which cannot achieve the true goal of carbon neutrality. Photothermal catalysis, as a novel conversion pathway, can achieve efficient CO2 conversion while significantly improving solar energy utilization. This review provides a detailed introduction of CO2 and H2 adsorption/activation and reaction pathways in thermal catalysis, as well as the catalytic mechanisms of thermal and chemical effects in photothermal catalytic RWGS to supply readers valuable insights on the mechanism of photothermal catalytic RWGS reaction and provide a reference for better catalyst design.

Green and rational design of Ln4Zn2L2 heteromultimetallic complexes for mild and highly efficient CO2 conversion

Reasonable and high efficient utilization of carbon dioxide (CO2) has always been considered as a kind of green and sustainable development strategy. However, the efficient chemical conversion of CO2 into value-added products has been limited due to lack of efficient catalysts. Herein, two novel heterometallic hexanuclear complex catalysts (viz Nd4Zn2L2 (1) and Eu4Zn2L2 (2)) were designed and synthesized, which featuring unique hetero-multinuclear units. The heterometallic hexanuclear complex catalysts not only have multi-bimetallic catalytic sites (Ln3+ and Zn2+) which can absorb more molecules and be beneficial to the improvement of catalytic performance, but also have the potential to further expand the chemical fixation of CO2 with epoxides avoid the harsh reaction conditions. Using the synthesis of propylene carbonate (PC) by cycloaddition reaction of propylene oxide (PO) and CO2 as a model reaction, the as-prepared catalysts and catalytic system showed high turnover frequencies (TOFs) under the mild condition instead of harsh reaction conditions. More importantly, these catalysts can be reused to preserve the structure's integrity and retain their catalytic activity at the same level even after five rounds of catalysis. The excellent regeneration performance indicated that the as-prepared heterometallic hexanuclear complex catalysts can be reused many times. In addition, the catalytic system also exhibited a wide range of substrates for epoxide. These results predict that the proposed heterometallic hexanuclear complex catalysts and catalytic system have great potential toward CO2 adsorption and catalytic conversion. This work may build up a new synthetic route for tailoring more new heterometallic complex catalysts with excellent catalytic activity and applied in various fields of application.

Optimizing Mo2C-based catalytic system for efficient CO2 conversion and CO selectivity through carbon-nitrogen supporting and potassium promotion

Preparing highly active, stable, and selective catalysts for the reverse water gas shift (RWGS) reaction is challenging because of the aggregation of the active catalyst at high RWGS reaction temperatures and deactivation of the active sites. Herein, we present a comparative evaluation and optimization of a molybdenum carbide system using a carbon-nitrogen (CN) support and alkali promotion. Hydrothermally prepared MoO3 nanorods were carburized at 700 °C using H2:CO (4:1) to prepare unsupported Mo2C, while CN-supported Mo2C (Mo2C@CN) was prepared using Mo-based metal-organic framework (Mo-MOF) as a sacrificial template. The as-prepared Mo2C@CN catalytic system was found to be highly active in the RWGS reaction in comparison with the unsupported Mo2C, where CO2 conversion percentage was around 76 % at 700 °C, combined with high CO selectivity (87 %) and very reduced CH4 selectivity (2 %). The addition of potassium as a promoter enhanced CO selectivity (99 %). The active catalyst performance was stable during the catalysis process and for up to 100 h, which imposes the effect of the CN support in preventing the aggregation of Mo2C and keeping its active sites in direct contact with the reactant. This work presents an effective strategy for improving the active catalyst dispersion and reducibility in synergy with the promoter effect to optimize the RWGS reaction output.

Co–N–C anchored g-C3N4 plate enhancing surface activity for efficient visible-light photocatalytic rhodamine-B elimination and CO2 conversion

Poor light-harvesting, fast recombination of photo-induced charge carriers, and unfavorable surface adsorption remain the major issues restricting the photocatalytic activity of g-C3N4. In this study, the Co-N-C decorated g-C3N4 (Co-N-C/g-CN) plate was developed by constructing Co-N-C on the surface of g-CN plate to improve photocatalytic rhodamine-B (RhB) degradation and CO2 conversion. The as-prepared 0.5Co-N-C/g-CN plate exhibited an exceptionally high efficiency in photocatalytic RhB degradation, with a rate of 99.5 % achieved in mere 30 min. Besides, the 0.5Co-N-C/g-CN plate also demonstrated an outstanding photocatalytic CO2 conversion rate of 33.7 μmol g−1cat h−1 within 4 h, which was more than 3.4-fold that of g-CN (9.9 μmol g−1cat h−1). Experiments demonstrated that the surface-constructed Co-N-C enhanced the visible light-harvesting and the separation of photo-induced charge carriers, boosting the optical property. Moreover, the density functionalized theory (DFT) calculations verified that the Co-N-C cocatalyst optimized O2 adsorption for the generation of superoxide radicals (·O-2), accelerating the photocatalytic RhB removal. Meanwhile, the Co-N-C was advantageous for the adsorption and activation of CO2, facilitating the photocatalytic CO2 conversion. This study provides a perspective on the surface engineering of g-CN toward enhanced photocatalytic performance.

Cobalt-based Polymerized Porphyrinic Network for Visible-light-driven CO2 Reduction.

Visible-light-driven conversion of carbon dioxide to valuable compounds and fuels is an important but challenging task due to the inherent stability of the CO2 molecules. Herein, we report a series of cobalt-based polymerized porphyrinic network (PPN) photocatalysts for CO2 reduction with high activity. The introduction of organic groups results in the addition of more conjugated electrons to the networks, thereby altering the molecular orbital levels within the networks. This integration of functional groups effectively adjusts the levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The PPN(Co)-NO2 exhibits outstanding performance, with a CO evolution rate of 12 268 μmol/g/h and 85.8% selectivity, surpassing most similar photocatalyst systems. The performance of PPN(Co)-NO2 is also excellent in terms of apparent quantum yield (AQY) for CO production (5.7% at 420 nm). Density functional theory (DFT) calculations, time-resolved photoluminescence (TRPL), and electrochemical tests reveal that the introduction of methyl and nitro groups leads to a narrower energy gap, facilitating a faster charge transfer. The coupling reaction in this study enables the formation of stable C-C bonds, enhancing the structural regulation, active site diversity, and stability of the catalysts for photocatalytic CO2 reduction. This work offers a facile strategy to develop reliable catalysts for efficient CO2 conversion.

High-efficient acetylene synthesis by selective electrochemical formation of CO2-derived CaC2

Acetylene can be used as feedstock for various chemical products, but its raw material has been a fossil fuel, which poses an environmental challenge. One way to address the challenge is to form CaC2 from CO2, which reacts with water to form acetylene. This study demonstrated the selective formation of CaC2 from CO2 by an electrochemical process in NaCl-KCl-CaCl2-CaO melt at 823 K to produce C2H2 with high current efficiency. The CaC2 was formed through two reactions: the carbon electrodeposition from CO2-derived CO32− (Step 1) and the electrochemical reduction of Ca(II) ion on the carbon (Step 2). These two reactions could be controlled by conducting potentiostatic electrolysis under CO2 and Ar atmospheres, resulting in acetylene synthesis with a maximum current efficiency of 92 %. Each electrochemical reaction agreed with the thermodynamic electrode potential. The electrolysis on carbon electrodes revealed that the higher the crystallinity of carbon, the more selectively CaC2 was formed. The CaC2 formation was induced by the reduction of Ca(II) ions on the basal plane of the graphite layer rather than the edge plane. The unique interfacial phenomenon between high-temperature melt and a carbon electrode surface will contribute to realizing a highly efficient CO2 conversion process to acetylene.

Solar Carboxylation Using CO2: Interfacially Synthesized Flexible Covalent Organic Frameworks Film as a Photocatalyst for Highly Selective Solar Carboxylation of Arylamines with CO2.

Carbon dioxide (CO2) conversion into value-added chemicals/fuels by utilizing solar energy is a sustainable way to mitigate our dependence on fossil fuels and stimulate a carbon-neutral economy. However, the efficient and affordable conversion of CO2 is still an ongoing challenge. Here, we report an interfacially synthesized visible-light-active Ni(II)-integrated covalent organic frameworks (TaTpBpy-Ni COFs) film as a photocatalyst for efficient CO2 conversion into carboxylic acid under ambient conditions. Notably, the TaTpBpy-Ni COFs film showed excellent photocatalytic activity for the carboxylation of various arylamines with CO2 to the corresponding arylcarboxylic acid via C-N bond activation under solar-light irradiation. Moreover, this carboxylation protocol exhibits mild reaction conditions and good functional group tolerance without the necessity of using stoichiometric metallic reductants. This work shows a benchmark example of not only the interfacially synthesized COFs film used as a photocatalyst for solar-light energy utilization but also the selective solar chemical production system of arylcarboxylic acid directly from CO2.

Mesoporous Cu2O microspheres for highly efficient C2 chemicals production from CO2 electroreduction

Production of C2 chemicals (such as C2H4, C2H5OH, etc.) from CO2 electroreduction reaction (CO2ER) has been regarded as a promising route to solve the environmental problems and energy crisis. In this work, mesoporous Cu2O microspheres of ca. 700 nm diameter size with low crystallinity were fabricated to enable efficient conversion of CO2 to C2 chemicals by electrocatalytic reduction. It is revealed that compared with bulk Cu2O, the obtained mesoporous Cu2O microspheres have larger surface area, more grain boundaries and defects (unsaturated coordination sites), which facilitate the adsorption and stabilization of the important intermediates, such as *CO, on the route to C2 chemicals formation. As a result, the Faraday efficiency (FE) of C2 products reaches as high as 82.6 % and 78.5 % in an H-cell and a flow cell, respectively. In situ Raman and FT-IR spectra reveal that during CO2ER test there exists abundant *CO on the mesoporous Cu2O surface, thus increasing the opportunity of CC coupling. And the high coverage of *CO on catalyst surface during CO2ER protects and stabilizes the oxidation state of Cu species. This work demonstrates an effective strategy to introduce mesoporous structures and decreased crystallinity for improving the performance of CO2ER to C2 products.

Recent advances on surface modification of non-oxide photocatalysts towards efficient CO2 conversion

Recent advances on surface modification of non-oxide photocatalysts towards efficient CO2 conversion

S-scheme charge transfer and photoinduced self-heating effect synergistically enhance the solar-driven CO2 reduction over Cs3Bi2Br9/Bi2S3 hybrid

Photothermocatalytic CO2 reduction, which harnesses the solar power to not only supply heat input but also generate charge carriers, represents an attractive and sustainable approach for solar-to-fuel conversion. Herein, an innovative Cs3Bi2Br9/Bi2S3 (CBB/Bi2S3) hybrid catalyst was elaborately designed by an electrostatic-driven self-assembling approach, which can achieve the effect of “kill two birds with one stone”. On the one hand, Bi2S3 functions as a photothermal material owing to its photoinduced self-heating effect, which elevates the temperature of the catalyst for accelerating the catalytic reaction. On the other hand, Bi2S3 synchronously boosts charge separation by forming an S-scheme heterojunction with CBB, as revealed by first-principle simulation and a series of experimental techniques. Remarkably, the developed CBB/Bi2S3 hybrid affords an impressive CO production rate (RCO = 153.82 μmol g−1h−1) without any extra heat input. The present study can provide some enlightening guidance for developing high-performance photothermal catalysts for efficient CO2 conversion.

An improved boron-catalyzed cycloaddition of CO2 to epoxides for the production of five-membered cyclic carbonates under atmospheric versus high-pressure conditions

A series of novel boron-based compounds (boronate esters) (1–8) were designed and successfully synthesized by introducing 3-(bromomethyl)phenylboronic acid into the various cis-diols using a Dean-Stark trap to remove the water formed during the esterification reactions. The synthesized boron-based compounds were characterized by 1H, 13C, and 11B NMR, FT-IR, UV–Vis, LC-MS/MS, elemental analysis, TGA-DTA, and melting point measurement techniques. Additionally, the Lewis acidity of the synthesized boronate esters was investigated by the conventional Gutmann-Beckett test. After the boronate esters were characterized in detail by various spectroscopic techniques, these compounds have been used as organocatalysts for the highly efficient conversion of greenhouse gas CO2 to cyclic carbonates under atmospheric versus high-pressure conditions without any solvents. The best conversion was performed in the presence of an organoboron catalyst (3) and DMAP as cocatalyst, with a 90.0 % yield and 97.7 % selectivities under high reactor pressure and with a 45.2% yield and 97.4% selectivities under atmospheric conditions. In addition, after it was determined that the target organoboron catalysts showed high catalytic activity, the effects of epoxide, base, temperature, CO2 pressure, Lewis acidity, reaction time, and amount of catalyst and base on the catalytic conversion were investigated for these catalysts.

Impact of the Surface Microenvironment on the Redox Properties of a Co-Based Molecular Cathode for Selective Aqueous Electrochemical CO2-to-CO Reduction.

Electrode-confined molecular catalysts are promising systems to enable the efficient conversion of CO2 to useful products. Here, we describe the development of an original molecular cathode for CO2 reduction to CO based on the noncovalent integration of a tetraazamacrocyclic Co complex to a carbon nanotube-based matrix. Aqueous electrochemical characterization of the modified electrode allowed for clear observation of a change of redox behavior of the Co center as surface concentration was tuned, highlighting the impact of the catalyst microenvironment on its redox properties. The molecular cathode enabled efficient CO2-to-CO conversion in fully aqueous conditions, giving rise to a turnover number (TONCO) of up to 20 × 103 after 2 h of constant electrolysis at a mild overpotential (η = 450 mV) and with a faradaic efficiency for CO of about 95%. Post operando measurements using electrochemical techniques, inductively coupled plasma, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy characterization of the films demonstrated that the catalysis remained of molecular nature, making this Co-based electrode a new promising alternative for molecular electrocatalytic conversion of CO2-to-CO in fully aqueous media.

Atomic Design of Copper Active Sites in Pristine Metal-Organic Coordination Compounds for Electrocatalytic Carbon Dioxide Reduction.

Electrocatalytic carbon dioxide reduction reaction (CO2RR) has emerged as a promising and sustainable approach to cut carbon emissions by converting greenhouse gas CO2 to value-added chemicals and fuels. Metal-organic coordination compounds, especially the copper (Cu)-based coordination compounds, which feature well-defined crystalline structures and designable metal active sites, have attracted much research attention in electrocatalytic CO2RR. Herein, the recent advances of electrochemical CO2RR on pristine Cu-based coordination compounds with different types of Cu active sites are reviewed. First, the general reaction pathways of electrocatalytic CO2RR on Cu-based coordination compounds are briefly introduced. Then the highly efficient conversion of CO2 on various kinds of Cu active sites (e.g., single-Cu site, dimeric-Cu site, multi-Cu site, and heterometallic site) is systematically discussed, along with the corresponding catalytic reaction mechanisms. Finally, some existing challenges and potential opportunities for this research direction are provided to guide the rational design of metal-organic coordination compounds for their practical application in electrochemical CO2RR.

Constructing an Asymmetric Covalent Triazine Framework to Boost the Efficiency and Selectivity of Visible-Light-Driven CO2 Photoreduction.

The photocatalytic reduction of CO2 represents an environmentally friendly and sustainable approach for generating valuable chemicals. In this study, a thiophene-modified highly conjugated asymmetric covalent triazine framework (As-CTF-S) is developed for this purpose. Significantly, single-component intramolecular energy transfer can enhance the photogenerated charge separation, leading to the efficient conversion of CO2 to CO during photocatalysis. As a result, without the need for additional photosensitizers or organic sacrificial agents, As-CTF-S demonstrates the highest photocatalytic ability of 353.2µmolg-1 and achieves a selectivity of ≈99.95% within a 4h period under visible light irradiation. This study provides molecular insights into the rational control of charge transfer pathways for high-efficiency CO2 photoreduction using single-component organic semiconductor catalysts.

Plasma Chemical Looping: Unlocking High-Efficiency CO2 Conversion to Clean CO at Mild Temperatures.

We propose a plasma chemical looping CO2 splitting (PCLCS) approach that enables highly efficient CO2 conversion into O2-free CO at mild temperatures. PCLCS achieves an impressive 84% CO2 conversion and a 1.3 mmol g-1 CO yield, with no O2 detected. Crucially, this strategy significantly lowers the temperature required for conventional chemical looping processes from 650 to 1000 °C to only 320 °C, demonstrating a robust synergy between plasma and the Ce0.7Zr0.3O2 oxygen carrier (OC). Systematic experiments and density functional theory (DFT) calculations unveil the pivotal role of plasma in activating and partially decomposing CO2, yielding a mixture of CO, O2/O, and electronically/vibrationally excited CO2*. Notably, these excited CO2* species then efficiently decompose over the oxygen vacancies of the OCs, with a substantially reduced activation barrier (0.86 eV) compared to ground-state CO2 (1.63 eV), contributing to the synergy. This work offers a promising and energy-efficient pathway for producing O2-free CO from inert CO2 through the tailored interplay of plasma and OCs.

Investigating the influence of oxygen doping in modulating product distribution for electrocatalytic CO2 reduction reaction

Efficient carbon recycling hinges on a comprehensive understanding of the mechanics behind electrocatalytic carbon dioxide reduction reactions (ECO2RR). Here, we have engineered, in-situ growth of CuO featured on O-doped gCN (COG) and ex-situ growth of CuO on bare gCN (CG) respectively, functioned as platforms fordisengaging the fundamental of ECO2RR. The COG holds substantial capacity compared to CG for efficient conversion of CO2 into hydrocarbons and initiated the C2 product pathway with enlarged faradaic efficiency (FE). The experimental results indicate that the COG enhanced the product conversion of CH3OH (FE = 61.5% ± 0.5), C2H5OH (FE = 24.7% ± 0.5), and HCOO– (FE = 6.1% ± 0.5) at −1.1 V Vs RHE. Meanwhile, the CG exhibited the maximum conversion of CO2 into CH3OH (FE = 56.4% ± 0.5) at the same potential range. For the CG, the partial current density of CH3OH (JCH3OH) is −1.8 mA cm−2, whereas COG exhibited −4.9 mA cm−2. Interestingly, in this ECO2RR, the study of oxygen doping demonstrated that feasible CO2 conversion, due to its affinity towards CO2 and high donor density.

A bifunctional catalyst derived from copper metal−organic framework for highly selective photocatalytic CO2 reduction and CO2 cycloaddition reaction

Highly efficient conversion of CO2 into valuable chemicals using green chemical reactions is attractive to the alleviation of global warming. Developing active catalysts with high selectivity remains challenging and is still in pursuit. Herein, a Cu-based metal−organic framework was successfully synthesized by a facile method and denoted as CuTIA. The obtained CuTIA with rich Lewis acid/base sites exhibited enhanced CO2 affinity and served as a bifunctional catalyst for CO2 conversion. To be specific, CuTIA converted CO2 into CH4 (103.78 μmol g−1 h−1) with a selectivity of 100 % under visible light irradiation. Besides, CuTIA drove CO2 cycloaddition reaction with epoxides to produce cyclic carbonates with a yield almost 100 % under mild conditions. This study provides a new perspective in the fabrication of bifunctional catalysts for enhancing CO2 conversion.

Plasma-Driven Efficient Conversion of CO2 and H2O into Pure Syngas with Controllable Wide H2/CO Ratios over Metal-Organic Frameworks Featuring In Situ Evolved Ligand Defects.

While the mild production of syngas (a mixture of H2 and CO) from CO2 and H2O is a promising alternative to the coal-based chemical engineering technologies, the inert nature of CO2 molecules, unfavorable splitting pathways of H2O and unsatisfactory catalysts lead to the challenge in the difficult integration of high CO2 conversion efficiency with produced syngas with controllable H2/CO ratios in a wide range. Herein, we report an efficient plasma-driven catalytic system for mild production of pure syngas over porous metal-organic framework (MOF) catalysts with rich confined H2O molecules, where their syngas production capacity is regulated by the in situ evolved ligand defects and the plasma-activated intermediate species of CO2 molecules. Specially, the Cu-based catalyst system achieves 61.9 % of CO2 conversion and the production of pure syngas with wide H2/CO ratios of 0.05 : 1-4.3 : 1. As revealed by the experimental and theoretical calculation results, the in situ dynamic structure evolution of Cu-containing MOF catalysts favors the generation of coordinatively unsaturated metal active sites with optimized geometric and electronic characteristics, the adsorption of reactants, and the reduced energy barriers of syngas-production potential-determining steps of the hydrogenation of CO2 to *COOH and the protonation of H2O to *H.

Microwave-assisted fabrication of 1D/2D CeO2/Bi2MoO6 heterojunction for efficient photocatalytic CO2 reduction to CH3OH

Photocatalytic CO2 reduction to fuels via visible light is regarded as a highly promising sustainable technology to address resource depletion and environmental apprehensions. However, the elevation of photocatalytic performance is limited due to some drawbacks of isolated catalysts such as poor CO2 adsorption performance, inadequate utilization of visible light, and rapid recombination of photo-generated carriers. Herein, a series of novel heterojunction catalysts, 1D/2D CeO2/Bi2MoO6 (CBMO-X), were fabricated utilizing the microwave-assisted method for the photocatalytic reduction of CO2. The CH3OH yield of the optimized CBMO-10 composite material reached 4.31 μmol⋅g−1⋅h−1 with excellent stability and structural integrity. Through a series of characterizations, it was found that the introduced CeO2 nanorods served as bifunctional sites for CO2 adsorption and photoelectron accumulation, effectively promoting CO2 conversion under visible light. In addition, CBMO-X exhibited faster photo-generated carriers migration rate due to the formation of the II-scheme heterojunction, which improved the photocatalytic performance obviously. Furthermore, the density functional theory (DFT) calculations and in situ XPS were used to investigate the carrier migration paths on the surface of composite materials. This work provided a novel strategy for the design of photocatalysts for efficient CO2 conversion.