Ionic Lignin Polymers for Controlled CO2 Capture, Release, and Conversion into High-Value Chemicals

In this study, an innovative and cost-effective ionic polymer for CO2 capture and utilization for the first time, using abundant and nonfood-based biomass lignin is reported. The modified ionic polymer synthesizes through the reaction of glycidyltrimethylammonium chloride with lignin under alkaline conditions to yield quaternary ammonium ionic functionality. Subsequently, the hydroxide-based pure ionic lignin polymer is employed for CO2 capture from both direct air and concentrated CO2 sources at room temperature and atmospheric pressure. Structural characterization of the polymers is accomplished through 1H, 13C, and 2D-heteronuclear single quantum coherence (HSQC) NMR, and FT-IR spectroscopy. The CO2 capture process is established through the formation of bicarbonate ions alongside the presence of CO2. The captured CO2 is precisely quantified by using inverse-gated proton decoupled 13C NMR with an internal standard (trioxane). Remarkably, the captured-CO2 amounts of ionic lignin polymer are 1.06 mmol g-1 (47 mg g-1) from concentrated-CO2 source and 0.60 mmol g-1 (26 mg g-1) from direct-air. The captured-CO2 in ionic lignin polymer is released in controlled manner and utilized in the synthesis of cyclic carbonate, showcasing the productive application of the captured carbon. Moreover, the fully controlled recovering of ionic lignin polymer achieves via repeated CO2 release ↔ CO2 capture.

Carbon Dioxide Capture by Niobium Polyoxometalate Fragmentation

High oxidation state metal cations in the form of oxides, oxoanions, or oxoperoxoanions have diverse roles in carbon dioxide removal (direct air capture and point source). Features include providing basic oxygens for chemisorption reactions, direct binding of carbonate, and catalyzing low-temperature CO2 release to regenerate capture media. Moreover, metal oxides and aqueous metal-oxo species are stable in harsh, point-source conditions. Here, we demonstrate aqueous niobium polyoxometalate (POM) carbon capture ability, specifically [Nb6O19]8-, Nb6. Upon exposure of aqueous Nb6 to CO2, Nb6 fragments and binds chemisorbed carbonate, evidenced by crystallization of Nb-carbonate POMs including [Nb22O53(CO3)16]28-and [Nb10O25(CO3)6]12-. While Rb/Cs+ counter cations yield crystal structures to understand the chemisorption processes, K+ counter cations enable higher capture efficiency (based on CO3/Nb ratio), determined by CHN analysis and thermogravimetry-mass spectrometry of the isolated solids. Sum frequency generation spectroscopy also showed higher carbon capture efficiency of the K-Nb6 solutions at the air-water interface, while small-angle X-ray scattering (SAXS) provided insights into the role of the alkalis in influencing these processes. Tetramethylammonium counter cations, like K+, demonstrate high efficiency of carbonate chemisorption at the interface, but SAXS and Raman of the bulk showed a predominance of a Nb24-POM (HxNb24O72, x ∼ 9) that does not bind carbonate. Control experiments show that carbonate detected at the interface is Nb-bound, and the Nb-carbonate species are stabilized by alkalis, demonstrating their supporting role in aqueous Nb-POM CO2 chemisorption. Of fundamental importance, this study presents rare examples of directing POM speciation with a gas, instead of liquid phase acid or base.

Photo-to-Thermal Conversion Harnessing Low-Energy Photons Renders Efficient Solar CO2 Reduction

Efficient photocatalytic solar CO2 reduction presents a challenge because visible-to-near-infrared (NIR) low-energy photons account for over 50% of solar energy. Consequently, they are unable to instigate the high-energy reaction necessary for dissociating C═O bonds in CO2. In this study, we present a novel methodology leveraging the often-underutilized photo-to-thermal (PTT) conversion. Our unique two-dimensional (2D) carbon layer-embedded Mo2C (Mo2C-Cx) MXene catalyst in black color showcases superior near-infrared (NIR) light absorption. This enables the efficient utilization of low-energy photons via the PTT conversion mechanism, thereby dramatically enhancing the rate of CO2 photoreduction. Under concentrated sunlight, the optimal Mo2C-C0.5 catalyst achieves CO2 reduction reaction rates of 12000-15000 μmol·g-1·h-1 to CO and 1000-3200 μmol·g-1·h-1 to CH4. Notably, the catalyst delivers solar-to-carbon fuel (STF) conversion efficiencies between 0.0108% to 0.0143% and the STFavg = 0.0123%, the highest recorded values under natural sunlight conditions. This innovative approach accentuates the exploitation of low-frequency, low-energy photons for the enhancement of photocatalytic CO2 reduction.

Boosting Formate Electrooxidation by Heterostructured PtPd Alloy and Oxides Nanowires

Direct formate fuel cells (DFFCs) receive increasing attention as promising technologies for the future energy mix and environmental sustainability, as formate can be made from carbon dioxide utilization and is carbon neutral. Herein, heterostructured platinum-palladium alloy and oxides nanowires (PtPd-ox NWs) with abundant defect sites are synthesized through a facile self-template method and demonstrated high activity toward formate electrooxidation reaction (FOR). The electronic tuning arising from the heterojunction between alloy and oxides influence the work function of PtPd-ox NWs. The sample with optimal work function reveals the favorable adsorption behavior for intermediates and strong interaction in the d-p orbital hybridization between Pt site and oxygen in formate, favoring the FOR direct pathway with a low energy barrier. Besides the thermodynamic regulation, the heterostructure can also provide sufficient hydroxyl species to facilitate the formation of carbon dioxide due to the ability of combining absorbed hydrogen and carbon monoxide at adjacent active sites, which contributes to the improvement of FOR kinetics on PtPd-ox NWs. Thus, heterostructured PtPd-ox NWs achieve dual regulation of FOR thermodynamics and kinetics, exhibiting remarkable performance and demonstrating potential in practical systems.

Reduction of CO2 in the presence of light via excited-state hydride transfer reaction in a NADPH-inspired derivative

The photo-catalytic reduction of CO2 into chemical feedstocks using solar energy has attracted vast interest in environmental science because of global warming. Based on our previous study on the CO2 complex with one of the benzimidazoline (BI) derivatives, we explore the photochemical reduction of CO2 in one of the benzimidazoline derivatives (1,3-dimethyl-5,6-diol-2,3-dihydro-1H-benzimidazole) by quantum-chemical methods. Our results reveal that carbon dioxide can be reduced to formate (HCOO-) by a hydride transfer reaction in the excited state of this complex of benzimidazoline derivative and CO2. While the ground-state hydride transfer reaction in this complex exhibits a substantial barrier, a charge-transfer can occur in the first singlet excited state of the complex in the UV-A region (326 nm), and after overcoming a moderate barrier (∼0.4 eV) the system can have access to the products. The interaction with a polar solvent decreases further the barrier such that the reaction in dimethyl sulfoxide can proceed with a negligibly small barrier (∼0.1 eV) or in a nearly barrierless manner. Our results show that this benzimidazoline derivative may act as a catalyst in the photoreduction of CO2.

Bifunctional Catalysts for CO2 Reduction and O2 Evolution: A Pivotal for Aqueous Rechargeable Zn-CO2 Batteries

The quest for the advancement of green energy storage technologies and reduction of carbon footprint is determinedly rising toward carbon neutrality. Aqueous rechargeable Zn-CO2 batteries (ARZCBs) hold the great potential to encounter both the targets simultaneously, i.e., green energy storage and CO2 conversion to value-added chemicals/fuels. The major descriptor of ARZCBs efficiency is allied with the reactions occurring at cathode during discharging (CO2 reduction) and charging (O2 evolution) which own different fundamental mechanisms and hence mandate the employment of two different catalysts. This presents an overall complex and expensive battery system which requires a concrete solution, while the development and application of a bifunctional cathode catalyst toward both reactions could reduce the complexity and cost and thus can be a pivotal for ARZCBs. However, despite the increasing research interest and ongoing research, a systematic evaluation of bifunctional catalysts is rarely reported. In this review, the need of bifunctional cathode catalysts for ARZCBs and associated challenges with strategies have been critically assessed. A detailed progress examination and understanding toward designing of bifunctional catalyst for ARZCBs have been provided. This review will enlighten the future research approaching boosted performance of ARZCBs through the development of efficient bifunctional cathode catalysts.

Revisiting Solar Energy Flow in Nanomaterial-Microorganism Hybrid Systems

Nanomaterial-microorganism hybrid systems (NMHSs), integrating semiconductor nanomaterials with microorganisms, present a promising platform for broadband solar energy harvesting, high-efficiency carbon reduction, and sustainable chemical production. While studies underscore its potential in diverse solar-to-chemical energy conversions, prevailing NMHSs grapple with suboptimal energy conversion efficiency. Such limitations stem predominantly from an insufficient systematic exploration of the mechanisms dictating solar energy flow. This review provides a systematic overview of the notable advancements in this nascent field, with a particular focus on the discussion of three pivotal steps of energy flow: solar energy capture, cross-membrane energy transport, and energy conversion into chemicals. While key challenges faced in each stage are independently identified and discussed, viable solutions are correspondingly postulated. In view of the interplay of the three steps in affecting the overall efficiency of solar-to-chemical energy conversion, subsequent discussions thus take an integrative and systematic viewpoint to comprehend, analyze and improve the solar energy flow in the current NMHSs of different configurations, and highlighting the contemporary techniques that can be employed to investigate various aspects of energy flow within NMHSs. Finally, a concluding section summarizes opportunities for future research, providing a roadmap for the continued development and optimization of NMHSs.

Removal of Carbon Dioxide and Hydrogen Sulfide from Natural Gas Using a Hybrid Solvent of Monoethanolamine and N-Methyl 2-Pyrrolidone

The main goal of traditional methods for sweetening natural gas (NG) is to remove hydrogen sulfide (H2S) and significantly lower carbon dioxide (CO2). However, when NG processes are integrated into the carbon capture and storage (CCS) framework, there is potential for synergy between these two technologies. A steady-state model utilizing a hybrid solvent consisting of N-methyl-2-pyrrolidone (NMP) and monoethanolamine (MEA) has been developed to successfully anticipate the CO2 and H2S capture process from NG. The model was tested against important variables affecting process performance. This article specifically explores the impact of operational parameters such as lean amine temperature, absorber pressure, and amine flow rate on the concentrations of CO2 and H2S in the sweet gas and reboiler duty. The result shows that hybrid solvents (MEA + NMP) perform better in removing acid gases and reducing reboiler duty than conventional chemical solvent MEA. The primary purpose is to meet product requirements while consuming the least energy possible, which is in line with any process plant's efficiency goals.

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.

Recent advances in heterogeneous catalysis of solar-driven carbon dioxide conversion

Solar-driven carbon dioxide (CO2) conversion including photocatalytic (PC), photoelectrochemical (PEC), photovoltaic plus electrochemical (PV/EC) systems, offers a renewable and scalable way to produce fuels and high-value chemicals for environment and energy sustainability. This review summarizes the basic fundament and the recent advances in the field of solar-driven CO2 conversion. Expanding the visible-light absorption is an important strategy to improve solar energy conversion efficiency. The separation and migration of photogenerated charges carriers to surface sites and the surface catalytic processes also determine the photocatalytic performance. Surface engineering including co-catalyst loading, defect engineering, morphology control, surface modification, surface phase junction, and Z-scheme photocatalytic system construction, have become fundamental strategies to obtain high-efficiency photocatalysts. Similar to photocatalysis, these strategies have been applied to improve the conversion efficiency and Faradaic efficiency of typical PEC systems. In PV/EC systems, the electrode surface structure and morphology, electrolyte effects, and mass transport conditions affect the activity and selectivity of electrochemical CO2 reduction. Finally, the challenges and prospects are addressed for the development of solar-driven CO2 conversion system with high energy conversion efficiency, high product selectivity and stability.

Nitrogen Configuration Effects on Charge Carrier Dynamics in CsPbBr3/Carbon Dots S-Scheme Heterojunction for Photocatalytic CO2 Reduction

Nitrogen-doped carbon dots (NCDs) featuring primary pyrrolic N and pyridinic N dominated configurations were prepared using hydrothermal (H-NCDs) and microwave (M-NCDs) methods, respectively. These H-NCDs and M-NCDs were subsequently applied to decorate CsPbBr3 nanocrystals (CPB NCs) individually, using a ligand-assisted reprecipitation process. Both CPB/M-NCDs and CPB/H-NCDs nanoheterostructures (NHSs) exhibited S-scheme charge transfer behavior, which enhanced their performance in photocatalytic CO2 reduction and selectivity of CO2-to-CH4 conversion, compared to pristine CPB NCs. The presence of pyrrolic N configuration at the heterojunction of CPB/H-NCDs facilitated efficient S-scheme charge transfer, leading to a remarkable 43-fold increase in photoactivity. In contrast, CPB/M-NCDs showed only a modest 3-fold enhancement in photoactivity, which was attributed to electron trapping by pyridinic N at the heterojunction. The study offers crucial insights into charge carrier dynamics within perovskite/carbon NHSs at the molecular level to advance the understanding of solar fuel generation.

Enhancing CO2 Electroreduction to C2 Products on Metal-Nitrogen Sites by Regulating H2O Dissociation

Water dissociation remarkably affects the CO2 reduction to CO and HCOOH, but whether it is effective for two-carbon product formation on M-Nx-containing catalysts is still ambiguous. Herein, by using a fluorinated metal phthalocyanine (MPc-F) as the M-N4-based model electrocatalyst, experimental and theoretical results reveal that the H2O-dissociation-induced active H species decrease the overpotential of the *CO hydrogenation to *CHO and facilitate the C-C coupling between *CHO and neighboring CO. Such an effect is strengthened by an increase in the *CO binding strength on the metal center. By introducing CuPc as the H2O dissociation catalyst into MPc-F (MPc-F/CuPc) to accurately regulate the H2O dissociation, the faradic efficiency of C2 products on FePc-F/CuPc and MnPc-F/CuPc increases from 0% (FePc-F and MnPc-F) to 26 and 36%, respectively. This work develops a novel strategy for enhancing the selectivity of M-Nx-containing catalysts to C2 products and reveals the correlation between H2O dissociation and C2 product formation.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron-Enriched Lattice Oxygen Species

Direct synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron-enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal-terminated phases in the crystal reconstruction process. Benefitting from the acid-base properties modulated by the electron-enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g-1 than the reported metal-oxide-based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron-enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron-enriched lattice oxygen can switch the rate-determining-step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

Research on carbon dioxide capture materials used for carbon dioxide capture, utilization, and storage technology: a review

In recent years, climate change has increasingly become one of the major challenges facing mankind today, seriously threatening the survival and sustainable development of mankind. Dramatically increasing carbon dioxide concentrations are thought to cause a severe greenhouse effect, leading to severe and sustained global warming, associated climate instability and unwelcome natural disasters, melting glaciers and extreme weather patterns. The treatment of flue gas from thermal power plants uses carbon capture, utilization, and storage (CCUS) technology, one of the most promising current methods to accomplish significant CO2 emission reduction. In order to implement the technological and financial system of CO2 capture, which is the key technology of CCUS technology and accounts for 70-80% of the overall cost of CCUS technology, it is crucial to create more effective adsorbents. Nowadays, with the development and application of various carbon dioxide capture materials, it is necessary to review and summarize carbon dioxide capture materials in time. In this paper, the main technologies of CO2 capture are reviewed, with emphasis on the latest research status of CO2 capture materials, such as amines, zeolites, alkali metals, as well as emerging MOFs and carbon nanomaterials. More and more research on CO2 capture materials has used a variety of improved methods, which have achieved high CO2 capture performance. For example, doping of layered double hydroxides (LDH) with metal atoms significantly increases the active site on the surface of the material, which has a significant impact on improving the CO2 capture capacity and performance stability of LDH. Although many carbon capture materials have been developed, high cost and low technology scale remain major obstacles to CO2 capture. Future research should focus on designing low-cost, high-availability carbon capture materials.

Overcoming Low C2+ Yield in Acidic CO2 Electroreduction: Modulating Local Hydrophobicity for Enhanced Performance

Operating electrochemical CO2 reduction reaction (CO2RR) in acidic media has garnered considerable attention due to its sustainable electrolyte cycling and stable performance. Nevertheless, the severe parasitic hydrogen evolution reaction (HER) and decayed multi-carbon species (C2+) yield still hampers efficient CO2RR in acid. Here, this work investigates the influence of local hydrophobicity on the acidic CO2RR. By employing direct electrodeposition, the hydrophobicity of the catalyst layer can be finely tuned over a wide range without additive. It is revealed that the hydrophobic microenvironment significantly suppressed HER, improved CO2RR performance and boosted C2+ yield. A Faradaic efficiency (FE) of ≈74% for C2+ is achieved in pH = 2 on electrodeposited copper with a highly hydrophobic environment. Moreover, this phenomenon can be extended to industrial application. An ≈81% total FE for the CO2RR, along with a ≈62% FE for C2+ species, is achieved even with commercial copper. Remarkably, the system exhibited stable operation for a continuous period exceeding 50 h at an industrially applied current density of 300 mA cm-2. This work highlights the crucial role of interface hydrophobicity in acidic CO2RR and proposes a facile and universally applicable method for achieving efficient and stable CO2RR to high-value products in acidic media.

Synergistic effects of core-shell poly(ionic liquids)@ZIF-8 nanocomposites for enhancing additive-free CO2 conversion

The present study, for the first time, reports the fabrication of core-shell poly(ionic liquids)@ZIF-8 nanocomposites through a facile in-situ polymerization strategy. These composites exhibited exceptional structural characteristics including high specific surface areas and the integration of high-density Lewis acid/base and nucleophilic active sites. The structure-activity relationship, reusability, and versatility of the poly(ionic liquids)@ZIF-8 composites were investigated for the cycloaddition reaction between CO2 and epoxide. By optimizing the composites structures and their catalytic performance, PIL-Br@ZIF-8(2:1) was identified as an exciting catalyst that exhibits high activity and selectivity in the synthesis of various cyclic carbonates under mild or even atmospheric pressure or simulated flue gas conditions. Moreover, the catalyst demonstrated excellent structural stability while maintaining its catalytic activity throughout multiple usage cycles. By combining DFT calculations, we investigated the transition states and intermediate geometries of the cycloaddition reaction in different coordination microenvironments, thereby proposing a synergistic catalytic mechanism involving multiple active sites.

Strategies for Enhancing the Photocatalytic and Electrocatalytic Efficiency of Covalent Triazine Frameworks for CO2 Reduction

Converting carbon dioxide (CO2) into fuel and high-value-added chemicals is considered a green and effective way to solve global energy and environmental problems. Covalent triazine frameworks (CTFs) are extensively utilized as an emerging catalyst for photo/electrocatalytic CO2 reduction reaction (CO2RR) recently recognized for their distinctive qualities, including excellent thermal and chemical stability, π-conjugated structure, rich nitrogen content, and a strong affinity for CO2, etc. Nevertheless, single-component CTFs have the problems of accelerated recombination of photoexcited electron-hole pairs and restricted conductivity, which limit their application for photo/electrocatalytic CO2RR. Therefore, emphasis will then summarize the strategies for enhancing the photocatalytic and electrocatalytic efficiency of CTFs for CO2RR in this paper, including atom doping, constructing a heterojunction structure, etc. This review first illustrates the synthesis strategies of CTFs and the advantages of CTFs in the field of photo/electrocatalytic CO2RR. Subsequently, the mechanism of CTF-based materials in photo/electrocatalytic CO2RR is described. Lastly, the challenges and future prospects of CTFs in photo/electrocatalytic CO2RR are addressed, which offers a fresh perspective for the future development of CTFs in photo/electrocatalytic CO2RR.

Physics-Based Machine Learning Models Predict Carbon Dioxide Solubility in Chemically Reactive Deep Eutectic Solvents

Carbon dioxide (CO2) is a detrimental greenhouse gas and is the main contributor to global warming. In addressing this environmental challenge, a promising approach emerges through the utilization of deep eutectic solvents (DESs) as an ecofriendly and sustainable medium for effective CO2 capture. Chemically reactive DESs, which form chemical bonds with the CO2, are superior to nonreactive, physically based DESs for CO2 absorption. However, there are no accurate computational models that provide accurate predictions of the CO2 solubility in chemically reactive DESs. Here, we develop machine learning (ML) models to predict the solubility of CO2 in chemically reactive DESs. As training data, we collected 214 data points for the CO2 solubility in 149 different chemically reactive DESs at different temperatures, pressures, and DES molar ratios from published work. The physics-driven input features for the ML models include σ-profile descriptors that quantify the relative probability of a molecular surface segment having a certain screening charge density and were calculated with the first-principle quantum chemical method COSMO-RS. We show here that, although COSMO-RS does not explicitly calculate chemical reaction profiles, the COSMO-RS-derived σ-profile features can be used to predict bond formation. Of the models trained, an artificial neural network (ANN) provides the most accurate CO2 solubility prediction with an average absolute relative deviation of 2.94% on the testing sets. Overall, this work provides ML models that can predict CO2 solubility precisely and thus accelerate the design and application of chemically reactive DESs.

Three-phase equilibria of hydrates from computer simulation. II. Finite-size effects in the carbon dioxide hydrate

In this work, the effects of finite size on the determination of the three-phase coexistence temperature (T3) of the carbon dioxide (CO2) hydrate have been studied by molecular dynamic simulations and using the direct coexistence technique. According to this technique, the three phases involved (hydrate-aqueous solution-liquid CO2) are placed together in the same simulation box. By varying the number of molecules of each phase, it is possible to analyze the effect of simulation size and stoichiometry on the T3 determination. In this work, we have determined the T3 value at 8 different pressures (from 100 to 6000 bar) and using 6 different simulation boxes with different numbers of molecules and sizes. In two of these configurations, the ratio of the number of water and CO2 molecules in the aqueous solution and the liquid CO2 phase is the same as in the hydrate (stoichiometric configuration). In both stoichiometric configurations, the formation of a liquid drop of CO2 in the aqueous phase is observed. This drop, which has a cylindrical geometry, increases the amount of CO2 available in the aqueous solution and can in some cases lead to the crystallization of the hydrate at temperatures above T3, overestimating the T3 value obtained from direct coexistence simulations. The simulation results obtained for the CO2 hydrate confirm the sensitivity of T3 depending on the size and composition of the system, explaining the discrepancies observed in the original work by Míguez et al. [J. Chem Phys. 142, 124505 (2015)]. Non-stoichiometric configurations with larger unit cells show a convergence of T3 values, suggesting that finite-size effects for these system sizes, regardless of drop formation, can be safely neglected. The results obtained in this work highlight that the choice of a correct initial configuration is essential to accurately estimate the three-phase coexistence temperature of hydrates by direct coexistence simulations.

Fabrication of -SO3H-functionalized polyphosphazene-reinforced proton conductive matrix-mixed membranes

Proton exchange membranes (PEMs) have emerged as very promising membranes for automotive applications because of their notable proton conductivity at low temperatures. These membranes find extensive utilization in fuel cells. Several polymeric materials have been used, but their application is constrained by their expense and intricate synthetic processes. Affordable and efficient synthetic methods for polymeric materials are necessary for the widespread commercial use of PEM technology. The polymeric combination of hexachlorocyclotriphosphazene (HCCP) and 4,4-diamino-2,2-biphenyldisulfonic acid facilitated the synthesis of PP-(PhSO3H)2, a polyphosphazene with built-in -SO3H moieties. Characterization revealed that it was a porous organic polymer with high stability. PP-(PhSO3H)2 exhibited a proton conductivity of up to 8.24 × 10-2 S cm-1 (SD = ±0.031) at 353 K under 98% relative humidity (RH), which was more than two orders of magnitude higher than that of its -SO3H-free analogue, PP-(Ph)2 (2.32 × 10-4 S cm-1) (SD = ±0.019) under identical conditions. Therefore, for application in a PEM fuel cell, PP-(PhSO3H)2-based matrix-mixed membranes (PP-(PhSO3H)2-MMMs) were fabricated by mixing them with polyacrylonitrile (PAN) in various ratios. The proton conductivity could reach up to 6.11 × 10-2 S cm-1 (SD = ±0.0048) at 353 K and 98%RH, when the weight ratio of PP-(PhSO3H)2 : PAN was 3 : 1, the value of which was comparable with those of commercially available electrolytes used in PEM fuel cells. PP-(PhSO3H)2-MMM (3 : 1) had an extended lifetime of reusability. Using phosphazene and bisulfonated multiple-amine modules as precursors, we demonstrated that a porous organic polymer with a highly effective proton-conductive matrix-mixed membrane for PEM fuel cells could be produced readily by an intuitive polymeric reaction.

Efficient Selective Carbon Dioxide Separation via Task-Specific Ionic Liquids Incorporated in ZIF-8

Owing to the rapid increase in anthropogenic emission of carbon dioxide (CO2) in the atmosphere, which has resulted in a number of global climate challenges, a decrease in CO2 emissions is urgently needed in the current scenario. This study focuses on the development and characterization of composites for carbon dioxide (CO2) separation. The composites consist of two task-specific ionic liquids (TSILs), namely, tetramethylgunidinium imidazole [TMGHIM] and tetramethylgunidinium phenol [TMGHPhO], impregnated in ZIF-8. The performance of CO2 separation, including sorption capacity and selectivity, was evaluated for pristine ZIF-8 and composites of TMGHIM@ZIF-8 and TMGHPhO@ZIF-8. To demonstrate the thermal stability of the material, thermogravimetric analysis (TGA) was performed. Additionally, powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to showcase the crystal structures and morphology. Fourier transform infrared spectroscopy (FTIR) and BET were also utilized to confirm the successful incorporation of TSILs into ZIF-8. The composite synthesized with TMGHIM@ZIF-8 demonstrated superior CO2 sorption performance as compared with TMGHPhO@ZIF-8. This is attributed to its strong attraction toward CO2, resulting in a higher CO2/CH4 selectivity of 110 while pristine MOFs showed 12 that is 9 times higher than that of the pristine ZIF-8. These TSILs@ZIF-8 composites have significant potential in designing sorbent materials for efficient acid gas separation applications.

Binding Strengths and Orientations in CO2 Adsorption on Cationic Scandium Oxides: Governing Factor Revealed by a Combined Infrared Spectroscopy and Theoretical Study

Carbon dioxide (CO2) adsorption is a critical step to curbing carbon emissions from fossil fuel combustion. Among various options, transition metal oxides have received extensive attention as promising CO2 adsorbents due to their affordability and sustainability for large-scale use. Here, the nature of binding interactions between CO2 molecules and cationic scandium oxides of different sizes, i.e., ScO+, Sc2O2+, and Sc3O4+, is investigated by mass-selective infrared photodissociation spectroscopy combined with quantum chemical calculations. The well-accepted electrostatic considerations failed to provide explanations for the trend in the binding strengths and variations in the binding orientations between CO2 and metal sites of cationic scandium oxides. The importance of orbital interactions in the driving forces for CO2 adsorption on cationic scandium oxides was revealed by energy decomposition analyses. A molecular surface property, known as the local electron attachment energy, is introduced to elucidate the binding affinity and orientation-specific reactivity of cationic scandium oxides upon the CO2 attachment. This study not only reveals the governing factor in the binding behaviors of CO2 adsorption on cationic scandium oxides but also serves as an archetype for predicting and rationalizing favorable binding sites and orientations in extended surface-adsorbate systems.

Capture and Utilization of CO2 with Morpholine for Effective Photocatalytic N-Formylmorpholine Production

Converting into high-value-added products represents the most optimal approach to CO2 utilization. The substitution of CO with CO2 as a potential critical material for formamide production is widely regarded as an ideal pathway and has garnered significant attention. However, high temperatures and pressures remain essential for the reaction, exerting a substantial influence on the utilization process. Herein, N-formylmorpholine was creatively synthesized by integrating the capture and solar-driven utilization of CO2 with morpholine. Notably, a remarkable N-formylmorpholine yield of 11433.3 μmol·h-1·g-1 was obtained, surpassing pure MoO3 by an astounding factor of 89.1 with a N-formylmorpholine yield of 63.8 μmol in 6 h, which is an astonishing increase of 57.5 times compared to MoO3. Both experimental results and density functional theory calculations suggest that the inclusion of Fe can effectively reduce the formation energy barrier while facilitating the desorption process of N-formylmorpholine, thereby optimizing the overall performance.

Triethanolamine-modified layered double oxide for efficient CO2 capture with low regeneration energy

Various adsorbents for CO2 capture have been developed to mitigate the greenhouse effect. In this work, a novel CO2 adsorbent was fabricated by depositing triethanolamine (TEOA) onto the surface of nickel-cobalt-aluminum layered double oxide (NiCoAl-LDO) via the impregnation method. The CO2 capacity of the TEOA-LDO composite reached 1.27 mmol/g at 0 °C and 100 kPa, which was twice that of unmodified NiCoAl-LDO. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the hydroxyl groups (-OH) on the surface of NiCoAl-LDO played a significant role in facilitating CO2 adsorption, similar to CO2 adsorption in the presence of H2O, where CO2 is not converted to carbamates but to bicarbonates through base-catalyzed hydration. This bicarbonate pathway doubles the theoretical amine efficiency, increases the CO2 capacity, and reduces the energy consumption during CO2 desorption. The work provides valuable insights into the development of CO2 adsorbents with high capacity, excellent cycling stability, and low regeneration energy.

Conjugated Microporous Polymers for Catalytic CO2 Conversion

Rising carbon dioxide (CO2) levels in the atmosphere are recognized as a threat to atmospheric stability and life. Although this greenhouse gas is being produced on a large scale, there are solutions to reduction and indeed utilization of the gas. Many of these solutions involve costly or unstable technologies, such as air-sensitive metal-organic frameworks (MOFs) for CO2 capture or "non-green" systems such as amine scrubbing. Conjugated microporous polymers (CMPs) represent a simpler, cheaper, and greener solution to CO2 capture and utilization. They are often easy to synthesize at scale (a one pot reaction in many cases), chemically and thermally stable (especially in comparison with their MOF and covalent organic framework (COF) counterparts, owing to their amorphous nature), and, as a result, cheap to manufacture. Furthermore, their large surface areas, tunable porous frameworks and chemical structures mean they are reported as highly efficient CO2 capture motifs. In addition, they provide a dual pathway to utilize captured CO2 via chemical conversion or electrochemical reduction into industrially valuable products. Recent studies show that all these attractive properties can be realized in metal-free CMPs, presenting a truly green option. The promising results in these two fields of CMP applications are reviewed and explored here.

Interfacial properties of the brine + carbon dioxide + oil + silica system

Molecular dynamics simulations of the H2O + CO2 + aromatic hydrocarbon and H2O + CO2 + benzene + silica (hydrophilic) systems are performed to gain insights into CO2-enhanced oil recovery (EOR) processes. For comparison purposes, an overview of the previous simulation studies of the interfacial properties of the brine + CO2 + alkane + silica system is also presented. In general, the water contact angle (CA) of the H2O + CO2 + silica (hydrophilic) system increased with pressure and decreased with temperature. The CAs of the H2O + hydrocarbon + silica (hydrophilic) system are not significantly affected by temperature and pressure. The simulated CAs were in the ranges of about 58°-77° and 81°-93° for the H2O + hexane + silica (hydrophilic) and the H2O + aromatic hydrocarbon + silica (hydrophilic) systems, respectively. In general, these CAs were not significantly influenced by the addition of CO2. The simulated CAs were in the ranges of about 51.4°-95.0°, 69.1°-86.0°, and 72.0°-87.9° for the brine + CO2 + silica (hydrophilic), brine + hexane + silica (hydrophilic), and brine + CO2 + hexane + silica (hydrophilic) systems, respectively. All these CAs increased with increasing NaCl concentration. The adhesion tension of the brine + silica (hydrophilic) system in the presence of CO2 and/or hexane decreased with increasing salt concentration. The simulated CAs were in the range of about 117°-139° for the H2O + alkane + silica (hydrophobic) system. These CAs are increased by the addition of CO2. At high pressures, the distributions of H2O normal to the silica (hydrophobic) surface in the droplet region of the H2O + silica system were found to be strongly affected by the presence of CO2. These insights might be key for optimizing the performance of the miscible CO2 water-alternating-gas injection schemes widely used for EOR.

Polyarene Oxides with Tunable Quinone Units for Photocatalytic CO2 Reduction: A Simple Strategy toward Effective and Selective Catalysts

The photocatalytic transformation of carbon dioxide (CO2) into valuable chemicals is a challenging process that requires effective and selective catalysts. However, most polymer-based photocatalysts with electron donor-acceptor (D-A) structures are synthesized with a fixed D-A ratio by using expensive monomers. Herein, we report a simple strategy to prepare polyarene oxides (PAOs) with quinone structural units via oxidation treatment of polyarene (PA). The resultant PAOs show tunable D-A structures and electronic band positions depending on the degree of oxidation, which can catalyze the photoreduction of CO2 with water under visible light irradiation, generating CO as the sole carbonaceous product without H2 generation. Especially, the PAO with an oxygen content of 17.6% afforded the highest CO production rate of 161.9 μmol g-1 h-1. It is verified that the redox transformation between quinone and phenolic hydroxyl in PAOs achieves CO2 photoreduction coupled with water oxidation. This study provides a facile way to access conjugated polymers with a tunable D-A structure and demonstrates that the resultant PAOs are promising photocatalysts for CO2 reduction.

Well-defined diatomic catalysis for photosynthesis of C2H4 from CO2

Owing to the specific electronic-redistribution and spatial proximity, diatomic catalysts (DACs) have been identified as principal interest for efficient photoconversion of CO2 into C2H4. However, the predominant bottom-up strategy for DACs synthesis has critically constrained the development of highly ordered DACs due to the random distribution of heteronuclear atoms, which hinders the optimization of catalytic performance and the exploration of actual reaction mechanism. Here, an up-bottom ion-cutting architecture is proposed to fabricate the well-defined DACs, and the superior spatial proximity of CuAu diatomics (DAs) decorated TiO2 (CuAu-DAs-TiO2) is successfully constructed due to the compact heteroatomic spacing (2-3 Å). Owing to the profoundly low C-C coupling energy barrier of CuAu-DAs-TiO2, a considerable C2H4 production with superior sustainability is achieved. Our discovery inspires a novel up-bottom strategy for the fabrication of well-defined DACs to motivate optimization of catalytic performance and distinct deduction of heteroatom synergistically catalytic mechanism.

Cascade Electrocatalytic and Thermocatalytic Reduction of CO2 to Propionaldehyde

Electrochemical CO2 reduction can convert CO2 to value-added chemicals, but its selectivity toward C3+ products are very limited. One possible solution is to run the reactions in hybrid processes by coupling electrocatalysis with other catalytic routes. In this contribution, we report the cascade electrocatalytic and thermocatalytic reduction of CO2 to propionaldehyde. Using Cu(OH)2 nanowires as the precatalyst, CO2 /H2 O is reduced to concentrated C2 H4 , CO, and H2 gases in a zero-gap membrane electrode assembly (MEA) reactor. The thermochemical hydroformylation reaction is separately investigated with a series of rhodium-phosphine complexes. The best candidate is identified to be the one with the 1,4-bis(diphenylphosphino)butane diphosphine ligand, which exhibits a propionaldehyde turnover number of 1148 under a mild temperature and close-to-atmospheric pressure. By coupling and optimizing the upstream CO2 electroreduction and downstream hydroformylation reaction, we achieve a propionaldehyde selectivity of ~38 % and a total C3 oxygenate selectivity of 44 % based on reduced CO2 . These values represent a more than seven times improvement over the best prior electrochemical system alone or over two times improvement over other hybrid systems.

Mn-promoted MoS2 catalysts for CO2 hydrogenation: enhanced methanol selectivity due to MoS2/MnOx interfaces

Considering the alarming scenario of climate change, CO2 hydrogenation to methanol is considered a key process for phasing out fossil fuels by means of CO2 utilization. In this context, MoS2 catalysts have recently shown to be promising catalysts for this reaction, especially in the presence of abundant basal-plane sulfur vacancies and due to synergistic mechanisms with other phases. In this work, Mn-promoted MoS2 prepared by a hydrothermal method presents considerable selectivity for CO2 hydrogenation to methanol in comparison with pure MoS2 and other promoters such as K and Co. Interestingly, if CO is used as a carbon source for the reaction, methanol production is remarkably lower, which suggests the absence of a CO intermediate during CO2 hydrogenation to methanol. After optimization of synthesis parameters, a methanol selectivity of 64% is achieved at a CO2 conversion of 2.8% under 180 °C. According to material characterization by X-ray Diffraction and X-ray Absorption, the Mn promoter is present mainly in the form of MnO and MnCO3 phases, with the latter undergoing convertion to MnO upon H2 pretreatment. However, following exposure to reaction conditions, X-ray photoelectron spectroscopy suggests that higher oxidation states of Mn may be present at the surface, suggesting that the improved catalytic activity for CO2 hydrogenation to methanol arises from a synergy between MoS2 and MnOx at the catalyst surface.

Light-driven thermocatalytic CO2 reduction by CH4 on alumina-cluster-modified Ni nanoparticles with excellent durability and high light-to-fuel efficiency promoted by the photoactivation effect

Using inexhaustible solar energy to drive efficient light-driven thermocatalytic CO2 reduction by CH4 (DRM) is an attractive approach that can synchronously reduce the greenhouse effect and convert solar energy into fuels. However, it is often limited by the intense light intensity required to produce high fuel production rates, and the catalyst deactivation due to severe carbon deposition generated from side reactions. Herein, a nanostructure of alumina-cluster-modified Ni nanoparticles supported on Al2O3 nanorods (ACM-Ni/Al2O3) was synthesized, displaying good catalytic performance under focused UV-vis-IR illumination. By light-driven thermocatalytic DRM on ACM-Ni/Al2O3 at a reduced light intensity of 76.9 kW m-2, the high fuel production rates of H2 (rH2, 65.7 mmol g-1 min-1) and CO (rCO, 78.8 mmol g-1 min-1), as well as an efficient light-to-fuel efficiency (η, 26.3 %) are achieved without additional heating. The rH2 and rCO of light-driven thermocatalysis are 2.9 and 1.9 times higher, respectively, compared to conventional thermocatalysis at the same temperature. We have discovered that high light-driven thermocatalytic activity originates from the photoactivation effect, significantly reducing the apparent activation energy and facilitating C* oxidation as a decisive step in DRM. ACM-Ni/Al2O3 possesses excellent durability and exhibits an extremely low coking rate of 4.40 × 10-3 gc gcatalyst-1 h-1, which is 26.8 times lower than that of the reference sample without Al2O3 cluster modification (R-Ni/Al2O3). This is owing to a decrease in activation energies (Ea) of C* oxidation and an increase in Ea of C* polymerization by the surface modification of Ni nanoparticles with Al2O3 clusters, effectively inhibiting carbon deposition.

Implementing vanadium peroxides as direct air carbon capture materials

Direct air capture (DAC) removal of anthropogenic CO2 from the atmosphere is imperative to slow the catastrophic effects of global climate change. Numerous materials are being investigated, including various alkaline inorganic metal oxides that form carbonates via DAC. Here we explore metastable early d0 transition metal peroxide molecules that undergo stabilization via multiple routes, including DAC. Specifically here, we describe via experiment and computation the mechanistic conversion of A3V(O2)4 (tetraperoxovanadate, A = K, Rb, Cs) to first a monocarbonate VO(O2)2(CO3)3-, and ultimately HKCO3 plus KVO4. Single crystal X-ray structures of rubidium and cesium tetraperoxovanadate are reported here for the first time, likely prior-challenged by instability. Infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), 51V solid state NMR (nuclear magnetic resonance), tandem thermogravimetry-mass spectrometry (TGA-MS) along with calculations (DFT, density functional theory) all converge on mechanisms of CO2 capture and release that involve the vanadium centre, despite the end product of a 300 days study being bicarbonate and metavanadate. Electron Paramagnetic Resonance (EPR) Spectroscopy along with a wet chemical assay and computational studies evidence the presense of ∼5% adventitous superoxide, likely formed by peroxide reduction of vanadium, which also stabilizes via the reaction with CO2. The alkalis have a profound effect on the stability of the peroxovanadate compounds, stability trending K > Rb > Cs. While this translates to more rapid CO2 capture with heavier alkalis, it does not necessarily lead to capture of more CO2. All compounds capture approximately two equivalents CO2 per vanadium centre. We cannot yet explain the reactivity trend of the alkali peroxovanadates, because any change in speciation of the alkalis from reactions to product is not quantifiable. This study sets the stage for understanding and implementing transition metal peroxide species, including peroxide-functionalized metal oxides, for DAC.

Enhancing CO2/N2 and CH4/N2 separation performance by salt-modified aluminum-based metal-organic frameworks

The energy-saving separation of CO2/N2 and CH4/N2 in the energy industry facilitates the reduction of greenhouse gas emissions and replenishes energy resources, but is a challenging separation process. The trade-off between adsorption capacity and selectivity of the adsorbents is one of the key bottlenecks in adsorption separation technologies' large-scale application in the above separation task. Herein, we introduced a series of fluoroborate or fluorosilicate salts (Cu(BF4)2, Zn(BF4)2 and ZnSiF6) into the open coordination nitrogen sites of aluminum-based metal-organic frameworks (MOF-253) to create multiple binding sites to simultaneously enhance the adsorption capacity and selectivity for the target gas. By the synergistic adsorption effect of metal ions (Cu2+ or Zn2+) and fluorinated anions (BF4- or (SiF6)2-), the single-component adsorption capacity and selectivity of salt-modified MOF-253 (MOF-253@Cu(BF4)2, MOF-253@Zn(BF4)2 and MOF-253@ZnSiF6) for CO2 and CH4 were effectively improved when compared to pristine MOF-253 at 298 K and 1 bar. In addition, the salt-modified MOF-253 has a moderate adsorption heat (<30 kJ mol-1) which could be rapidly regenerated at low energy by evacuation desorption. As confirmed by the ambient breakthrough experiments of MOF-253 and MOF-253@ZnSiF6, the real separation performance for both CO2/N2 (1/4) and CH4/N2 (1/4) was obviously improved. This work provides a feasible post-modification strategy on uncoordinated sites of the framework to improve adsorption separation performance and promote the development of ideal adsorbents with a view to realizing their application in the energy industry.

Evaluation of the Hydrophilic/Hydrophobic Balance of 13X Zeolite by Adsorption of Water, Methanol, and Cyclohexane as Pure Vapors or as Mixtures

Adsorption isotherms of pure vapors and vapor mixtures of water, methanol, and cyclohexane were studied using a synthesized 13X zeolite (FAU topology), by means of a DVS gravimetric vapor analyzer. These results were validated by GCMC calculations. The surface chemistry of the adsorbent was characterized by the thermodesorption of ammonia, and its textural properties were studied using nitrogen physisorption. The 13X zeolite was found to be strongly acidic (BrØnsted acid sites, Si/Al = 1.3) and its specific surface area around 1100 m2·g-1. Water was found to be able to diffuse within both the supercages and the sodalite cavities of the FAU structure, whereas methanol and cyclohexane were confined in the supercages only. The water/methanol sorption selectivity of the 13X zeolite was demonstrated by co-adsorption measurements. The composition of the water/methanol adsorbed phase could be calculated by assuming IAST hypotheses. This model failed in the case of the water/cyclohexane co-adsorption system, which is in line with the non-miscibility of the components in the adsorbed state. The sorption isotherms could be successfully simulated, confirming the robustness of the forcefields used. The 13X zeolite confirmed its a priori expected hydrophilic nature, which is useful for the selective adsorption of water in a methanol-water vapor mixture.

Hollow carbon-based materials for electrocatalytic and thermocatalytic CO2 conversion

Electrocatalytic and thermocatalytic CO2 conversions provide promising routes to realize global carbon neutrality, and the development of corresponding advanced catalysts is important but challenging. Hollow-structured carbon (HSC) materials with striking features, including unique cavity structure, good permeability, large surface area, and readily functionalizable surface, are flexible platforms for designing high-performance catalysts. In this review, the topics range from the accurate design of HSC materials to specific electrocatalytic and thermocatalytic CO2 conversion applications, aiming to address the drawbacks of conventional catalysts, such as sluggish reaction kinetics, inadequate selectivity, and poor stability. Firstly, the synthetic methods of HSC, including the hard template route, soft template approach, and self-template strategy are summarized, with an evaluation of their characteristics and applicability. Subsequently, the functionalization strategies (nonmetal doping, metal single-atom anchoring, and metal nanoparticle modification) for HSC are comprehensively discussed. Lastly, the recent achievements of intriguing HSC-based materials in electrocatalytic and thermocatalytic CO2 conversion applications are presented, with a particular focus on revealing the relationship between catalyst structure and activity. We anticipate that the review can provide some ideas for designing highly active and durable catalytic systems for CO2 valorization and beyond.

Amine Adsorbents Stability for Post-Combustion CO2 Capture: Determination and Validation of Laboratory Degradation Rates in a Multi-staged Fluidized Bed Pilot Plant

Alternative to current liquid amine technologies for post-combustion CO2 capture, new technologies such as adsorbent-based processes are developed, wherein material lifetime and degradation is important. Herein a robust method to determine degradation rates in a laboratory setup is developed, which was validated with a continuous multi-staged fluidized bed pilot plant designed to capture 1 ton CO2 per day. An amine functionalized polystyrene adsorbent showed very good agreement between the experimental 1000-hour laboratory degradation rates and 2200 hours of degradation in a pilot plant. This validates how laboratory experiments can be extrapolated for sorbent screening and for scale-up. Resulting, the oxidative degradation in the desorber at high temperatures (120 °C) and low O2 concentrations (150 ppmv) is 3 times higher compared to the adsorber at low temperatures and high O2 (56 °C, 7 vol %). Laboratory degradation experiments can hence be used to further optimize process operations to limit degradation or screen for potential new adsorbents.

Wettability Engineering of Solar Methanol Synthesis

Engineering the wettability of surfaces with hydrophobic organics has myriad applications in heterogeneous catalysis and the large-scale chemical industry; however, the mechanisms behind may surpass the proverbial hydrophobic kinetic benefits. Herein, the well-studied In2O3 methanol synthesis photocatalyst has been used as an archetype platform for a hydrophobic treatment to enhance its performance. With this strategy, the modified samples facilitated the tuning of a wide range of methanol production rates and selectivity, which were optimized at 1436 μmol gcat-1 h-1 and 61%, respectively. Based on in situ DRIFTS and temperature-programmed desorption-mass spectrometry, the surface-decorated alkylsilane coating on In2O3 not only kinetically enhanced the methanol synthesis by repelling the produced polar molecules but also donated surface active H to facilitate the subsequent hydrogenation reaction. Such a wettability design strategy seems to have universal applicability, judged by its success with other CO2 hydrogenation catalysts, including Fe2O3, CeO2, ZrO2, and Co3O4. Based on the discovered kinetic and mechanistic benefits, the enhanced hydrogenation ability enabled by hydrophobic alkyl groups unleashes the potential of the surface organic chemistry modification strategy for other important catalytic hydrogenation reactions.

Carbon dioxide activation by discandium dioxide cations in the gas phase: a combined investigation of infrared photodissociation spectroscopy and DFT calculations

We present a combined computational and experimental study of CO2 activation at the Sc2O2+ metal oxide ion center in the gas phase. Density functional theory calculations on the structures of [Sc2O2(CO2)n]+ (n = 1-4) ion-molecule complexes reveal a typical end-on binding motif as well as bidentate and tridentate carbonate-containing configurations. As the number of attached CO2 molecules increases, activated forms tend to dominate the isomeric populations. Distortion energies are unveiled to account for the conversion barriers from molecularly bound isomers to carbonate structures, and show a monotonically decreasing trend with successive CO2 ligand addition. The infrared photodissociation spectra of target ion-molecule complexes were recorded in the 2100-2500 cm-1 frequency region and interpreted by comparison with simulated IR spectra of low-lying isomers representing distinct configurations, demonstrating a high possibility of carbonate structure formation in current experiments.

An Aqueous Redox Flow Battery Using CO2 as an Active Material with a Homogeneous Ir Catalyst

For the application of CO2 as an energy storage material, a H2 storage system has been proposed based on the interconversion of CO2 and formic acid (or formate). However, energy losses are inevitable in the conversion of electrical energy to H2 as chemical energy (≈70 % electrical efficiency) and H2 to electrical energy (≈40 % electrical efficiency). To overcome these significant energy losses, we developed a system based on the interconversion of CO2 and formate for the direct storage and generation of electricity. In this paper, we report an aqueous redox flow battery system using homogeneous Ir catalysts with CO2 -formate redox pair. The system exhibited a maximum discharge capacity of 10.5 mAh (1.5 Ah L-1 ), capacity decay of 0.2 % per cycle, and total turnover number of 2550 after 50 cycles. During charging-discharging, in situ fluorescence X-ray absorption fine structure spectroscopy based on an online setup indicated that the active species was in a high valence state of IrIV .

Stable Pyrene-Based Metal-Organic Framework for Cyclization of Propargylic Amines with CO2 and Detection of Antibiotics in Water

A pyrene-based metal-organic framework, Cd2(PTTB)(H2O)2 (WYU-11), was synthesized from the tetracarboxylic pyrene ligand H4PTTB (H4PTTB = 1,3,6,8-tetrakis(3-carboxyphenyl)pyrene) and Cd(NO3)2·4H2O. Powder X-ray diffraction analysis discloses that the framework is stable in acid, base, and various organic solvent environments. WYU-11 shows excellent catalytic performance on the cyclization reaction of propargylic amines with CO2 into 2-oxazolidinones under mild conditions (60 °C, atmospheric CO2). 1H NMR studies unveiled that WYU-11 and 1,1,3,3-tetramethylguanidine (TMG) can synergistically activate the propargylic amine substrate and promote the reaction. Importantly, WYU-11 represents a rare example of noble metal-free heterogeneous catalyst that can catalyze the cyclization of CO2 with propargylic amines. In addition, by virtue of the excellent water stability and luminescence properties, WYU-11 shows excellent detection performance for sulfathiazole (STZ) and ornidazole (ODZ) in water. Investigation reveals that the coexistence of photoinduced electron transfer and internal filtering effect could reasonably explain the luminescence quenching of WYU-11 by the antibiotics.

Three Robust Isoreticular Metal-Organic Frameworks with High-Performance Selective CO2 Capture and Separation

Based on the hard-soft acid base (HSAB) theory, three robust isoreticular metal-organic frameworks (MOFs) with nia topology were successfully synthesized by solvothermal reaction {[In3O(BHB)(H2O)3]NO3·3DMA (JLU-MOF110(In)), [Fe3O(BHB)(H2O)3]NO3 (JLU-MOF110(Fe)), and [Fe2NiO(BHB)(H2O)3] (JLU-MOF110(FeNi)) (DMA = N,N-dimethylacetamide, H6BHB = 4,4″-benzene-1,3,5-triyl-hexabenzoic acid)}. Both JLU-MOF110(In) and JLU-MOF110(Fe) are cationic frameworks, and their BET surface areas are 301 and 446 m2/g, respectively. By modification of the components of metal clusters, JLU-MOF110(FeNi) features a neutral framework, and the BET surface area is increased up to 808 m2/g. All three MOF materials exhibit high chemical and thermal stability. JLU-MOF110(In) remains stable for 24 h at pH values ranging from 1 to 11, while JLU-MOF110(Fe) and JLU-MOF110(FeNi) persist to be stable for 24 h at pH from 1 to 12. JLU-MOF110(In) exhibits thermal stability up to 350 °C, whereas JLU-MOF110(Fe) and JLU-MOF(FeNi) can be stable up to 300 °C. Thanks to the microporous cage-based structure and abundant open metal sites, JLU-MOF110(In), JLU-MOF110(Fe), and JLU-MOF110(FeNi) have excellent CO2 capture capacity (28.0, 51.5, and 99.6 cm3/g, respectively, under 298 K and 1 bar). Interestingly, the ideal adsorption solution theory results show that all three MOFs exhibit high separation selectivity toward CO2 over N2 (35.2, 43.2, and 43.2 for CO2/N2 = 0.15/0.85) and CO2 over CH4 (14.4, 11.5, and 10.1 for CO2/CH4 = 0.5/0.5) at 298 K and 1 bar. Thus, all three MOFs are potential candidates for CO2 capture and separation. Among them, JLU-MOF110(FeNi) displays the best separation potential, as revealed by dynamic column breakthrough experiments.

A semiconducting hybrid of RhOx/GaN@InGaN for simultaneous activation of methane and water toward syngas by photocatalysis

Prior to the eventual arrival of carbon neutrality, solar-driven syngas production from methane steam reforming presents a promising approach to produce transportation fuels and chemicals. Simultaneous activation of the two reactants, i.e. methane and water, with notable geometric and polar discrepancy is at the crux of this important subject yet greatly challenging. This work explores an exceptional semiconducting hybrid of RhOx/GaN@InGaN nanowires for overcoming this critical challenge to achieve efficient syngas generation from methane steam reforming by photocatalysis. By coordinating density functional theoretical calculations and microscopic characterizations, with in situ spectroscopic measurements, it is found that the multifunctional RhOx/GaN interface is effective for simultaneously activating both CH4 and H2O by stretching the C-H and O-H bonds because of its unique Lewis acid/base attribute. With the aid of energetic charge carriers, the stretched C-H and O-H bonds of reactants are favorably cleaved, resulting in the key intermediates, i.e. *CH3, *OH, and *H, to sit on Rh sites, Rh sites, and N sites, respectively. Syngas is subsequently produced via energetically favored pathway without additional energy inputs except for light. As a result, a benchmarking syngas formation rate of 8.1 mol·gcat-1·h-1 is achieved with varied H2/CO ratios from 2.4 to 0.8 under concentrated light illumination of 6.3 W·cm-2, enabling the achievement of a superior turnover number of 10,493 mol syngas per mol Rh species over 300 min of long-term operation. This work presents a promising strategy for green syngas production from methane steam reforming by utilizing unlimited solar energy.

Different reactor configurations for enhancement of CO2 methanation

Greenhouse gas emissions are a massive concern for scientists to minimize the effect of global warming in the environment. In this study, packed bed, coated wall, and membrane reactors were investigated using three novel nickel catalysts for the methanation of CO2. CFD modelling methodologies were implemented to develop 2D models. The validity of the model was investigated in a previous study where experimental and simulated results in a packed bed reactor were in a good agreement. It was observed that the coated wall reactor had poorer performance compared to the packed bed, approximately 30% difference between the results, as the residence time of the former was lower. In addition, two membrane configurations were proposed, including a membrane packed bed and membrane coated wall reactor. Additional studies were performed in the coated wall reactor revealing that lower flow rates lead to higher conversion values. As for the bed thickness the optimum layer was found to be 1 mm. In both membrane reactor configurations, the effect of the thickness of M1 membrane, which indicates the membrane for the removal of H2O, didn't show difference while the reduction of the thickness of M2 membrane, which indicates the membrane for the removal of CO2, H2 and H2O, showed better results in terms of conversion.

Selective Metal-Free CO2 Photoreduction in Water Using Porous Nanostructures with Internal Molecular Free Volume

The conversion of CO2 to a sole carbonaceous product using photocatalysis is a sustainable solution for alleviating the increasing levels of CO2 emissions and reducing our dependence on nonrenewable resources such as fossil fuels. However, developing a photoactive, metal-free catalyst that is highly selective and efficient in the CO2 reduction reaction (CO2RR) without the need for sacrificial agents, cocatalysts, and photosensitizers is challenging. Furthermore, due to the poor solubility of CO2 in water and the kinetically and thermodynamically favored hydrogen evolution reaction (HER), designing a highly selective photocatalyst is challenging. Here, we propose a molecular engineering approach to design a photoactive polymer with high CO2 permeability and low water diffusivity, promoting the mass transfer of CO2 while suppressing HER. We have incorporated a contorted triptycene scaffold with "internal molecular free volume (IMFV)" to enhance gas permeability to the active site by creating molecular channels through the inefficient packing of polymer chains. Additionally, we introduced a pyrene moiety to promote visible-light harvesting capability and charge separation. By leveraging these qualities, the polymer exhibited a high CO generation rate of 77.8 μmol g-1 h-1, with a high selectivity of ∼98% and good recyclability. The importance of IMFV was highlighted by replacing the contorted triptycene unit with a planar scaffold, which led to a selectivity reversal favoring HER over CO2RR in water. In situ electron paramagnetic resonance (EPR), time-resolved photoluminescence spectroscopy (TRPL), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques, further supported by theoretical calculations, were employed to enlighten the mechanistic insight for metal-free CO2 reduction to exclusively CO in water.

Synergistic investigation of natural and synthetic C1-trophic microorganisms to foster a circular carbon economy

A true circular carbon economy must upgrade waste greenhouse gases. C1-based biomanufacturing is an attractive solution, in which one carbon (C1) molecules (e.g. CO2, formate, methanol, etc.) are converted by microbial cell factories into value-added goods (i.e. food, feed, and chemicals). To render C1-based biomanufacturing cost-competitive, we must adapt microbial metabolism to perform chemical conversions at high rates and yields. To this end, the biotechnology community has undertaken two (seemingly opposing) paths: optimizing natural C1-trophic microorganisms versus engineering synthetic C1-assimilation de novo in model microorganisms. Here, we pose how these approaches can instead create synergies for strengthening the competitiveness of C1-based biomanufacturing as a whole.

Novel hybrid QSPR-GPR approach for modeling of carbon dioxide capture using deep eutectic solvents

In recent years, deep eutectic solvents (DESs) have garnered considerable attention for their potential in carbon capture and utilization processes. Predicting the carbon dioxide (CO2) solubility in DES is crucial for optimizing these solvent systems and advancing their application in sustainable technologies. In this study, we presented an evolving hybrid Quantitative Structure-Property Relationship and Gaussian Process Regression (QSPR-GPR) model that enables accurate predictions of CO2 solubility in various DESs. The QSPR-GPR model combined the strengths of both approaches, leveraging molecular descriptors and structural features of DES components to establish a robust and adaptable predictive framework. Through a systematic evolution process, we iteratively refined the model, enhancing its performance and generalization capacity. By incorporating experimental CO2 solubility data in varied DES compositions and temperatures, we trained the model to capture the intricate solubility behaviour precisely. The analytical capability of the evolving hybrid model was validated against an extensive dataset of experimental CO2 solubility values, demonstrating its superiority over individual QSPR and GPR models. The model achieves high accuracy, capturing the complex interactions between CO2 and DES components under varying thermodynamic conditions. The versatility of the evolving hybrid model was highlighted by its ability to accommodate new experimental data and adapt to different DES compositions and temperatures. The proposed QSPR-GPR model presented a powerful tool for predicting CO2 solubility in DES, providing valuable insights for designing and optimizing solvent systems in carbon capture technologies. The model's remarkable performance enhances our understanding of CO2 solubility mechanisms and contributes to sustainable solutions for mitigating greenhouse gas emissions. As research in DESs progresses, the evolving hybrid QSPR-GPR model offers a versatile and accurate means for predicting CO2 solubility, supporting advancements in carbon capture and utilization processes towards a greener and more sustainable future.

Liquid-in-Aerogel Porous Composite Allows Efficient CO2 Capture and CO2 /N2 Separation

The pursuit of efficient CO2 capture materials remains an unmet challenge. Especially, meeting both high sorption capacity and fast uptake kinetics is an ongoing effort in the development of CO2 sorbents. Here, a strategy to exploit liquid-in-aerogel porous composites (LIAPCs) that allow for highly effective CO2 capture and selective CO2 /N2 separation, is reported. Interestingly, the functional liquid tetraethylenepentamine (TEPA) is partially filled into the air pockets of SiO2 aerogel with left permanent porosity. Notably, the confined liquid thickness is 10.9-19.5 nm, which can be vividly probed by the atomic force microscope and rationalized by tailoring the liquid composition and amount. LIAPCs achieve high affinity between the functional liquid and solid porous counterpart, good structure integrity, and robust thermal stability. LIAPCs exhibit superb CO2 uptake capacity (5.44 mmol g-1 , 75 °C, and 15 vol% CO2 ), fast sorption kinetics, and high amine efficiency. Furthermore, LIAPCs ensure long-term adsorption-desorption cycle stability and offer exceptional CO2 /N2 selectivity both in dry and humid conditions, with a separation factor up to 1182.68 at a humidity of 1%. This approach offers the prospect of efficient CO2 capture and gas separation, shedding light on new possibilities to make the next-generation sorption materials for CO2 utilization.

The Effect of Alkali Metals (Li, Na, and K) on Ni/CaO Dual-Functional Materials for Integrated CO2 Capture and Hydrogenation

Ni/CaO, a low-cost dual-functional material (DFM), has been widely studied for integrated CO2 capture and hydrogenation. The core of this dual-functional material should possess both good CO2 capture-conversion performance and structural stability. Here, we synthesized Ni/CaO DFMs modified with alkali metals (Na, K, and Li) through a combination of precipitation and combustion methods. It was found that Na-modified Ni/CaO (Na-Ni/CaO) DFM offered stable CO2 capture-conversion activity over 20 cycles, with a high CO2 capture capacity of 10.8 mmol/g and a high CO2 conversion rate of 60.5% at the same temperature of 650 °C. The enhanced CO2 capture capacity was attributed to the improved surface basicity of Na-Ni/CaO. In addition, the incorporation of Na into DFMs had a favorable effect on the formation of double salts, which shorten the CO2 capture and release process and promoted DFM stability by hindering their aggregation and the sintering of DFMs.

Comparative study of CO2 insertion into pincer supported palladium alkyl and aryl complexes

The insertion of CO2 into metal alkyl bonds is a crucial elementary step in transition metal-catalyzed processes for CO2 utilization. Here, we synthesize pincer-supported palladium complexes of the type (tBuPBP)Pd(alkyl) (tBuPBP = B(NCH2PtBu2)2C6H4-; alkyl = CH2CH3, CH2CH2CH3, CH2C6H5, and CH2-4-OMe-C6H4) and (tBuPBP)Pd(C6H5) and compare the rates of CO2 insertion into the palladium alkyl bonds to form metal carboxylate complexes. Although, the rate constant for CO2 insertion into (tBuPBP)Pd(CH2CH3) is more than double the rate constant we previously measured for insertion into the palladium methyl complex (tBuPBP)Pd(CH3), insertion into (tBuPBP)Pd(CH2CH2CH3) occurs approximately one order of magnitude slower than (tBuPBP)Pd(CH3). CO2 insertion into the benzyl complexes (tBuPBP)Pd(CH2C6H5) and (tBuPBP)Pd(CH2-4-OMe-C6H4) is significantly slower than any of the n-alkyl complexes, and CO2 does not insert into the palladium phenyl bond of (tBuPBP)Pd(C6H5). While (tBuPBP)Pd(CH2CH3) and (tBuPBP)Pd(CH2CH2CH3) are resistant to β-hydride elimination, we were unable to synthesize complexes with n-butyl, iso-propyl, and tert-butyl ligands due to β-hydride elimination and an unusual reductive coupling, which involves the formation of new C-B bonds. This reductive process also occurred for (tBuPBP)Pd(CH2C6H5) at elevated temperature and a related process involving the formation of a new H-B bond prevented the isolation of (tBuPBP)PdH. DFT calculations provide insight into the relative rates of CO2 insertion and indicate that steric factors are critical. Overall, this work is one of the first comparative studies of the rates of CO2 insertion into different metal alkyl bonds and provides fundamental information that may be important for the development of new catalysts for CO2 utilization.

Nanoscale Janus Z-Scheme Heterojunction for Boosting Artificial Photosynthesis

Artificial photosynthesis for CO2 reduction coupled with water oxidation currently suffers from low efficiency due to inadequate interfacial charge separation of conventional Z-scheme heterojunctions. Herein, an unprecedented nanoscale Janus Z-scheme heterojunction of CsPbBr3 /TiOx is constructed for photocatalytic CO2 reduction. Benefitting from the short carrier transport distance and direct contact interface, CsPbBr3 /TiOx exhibits significantly accelerated interfacial charge transfer between CsPbBr3 and TiOx (8.90 × 108 s-1 ) compared with CsPbBr3 :TiOx counterpart (4.87 × 107 s-1 ) prepared by traditional electrostatic self-assembling. The electron consumption rate of cobalt doped CsPbBr3 /TiOx can reach as high as 405.2 ± 5.6 µmol g-1 h-1 for photocatalytic CO2 reduction to CO coupled with H2 O oxidation to O2 under AM1.5 sunlight (100 mW cm-2 ), over 11-fold higher than that of CsPbBr3 :TiOx , and surpassing the reported halide-perovskite-based photocatalysts under similar conditions. This work provides a novel strategy to boost charge transfer of photocatalysts for enhancing the performance of artificial photosynthesis.