Carbon capture and utilization (CCU) from blast furnace gas (BFG) is essential for reducing CO2 emissions in the iron and steel industry. This study proposes and evaluates a CCU process flowsheet to capture CO2 from BFG using vacuum pressure swing adsorption (VPSA) and produce methanol (MeOH) in a membrane reactor. Experimentally validated models of the membrane and WGS reactor, together with a surrogate model for VPSA to reduce the computational load, were integrated into the flowsheet. Multi-objective optimization confirmed a trade-off between MeOH productivity and energy consumption. The results further revealed that CO2-rich conditions and membrane-based product removal synergistically enhanced H2 conversion and MeOH productivity. The proposed surrogate model-based methodology provides a practical framework for designing membrane reactor-VPSA processes.
Ni/13X catalysts promoted with low Rh and Ru loadings were prepared on commercial 13X zeolite granules by low-water dropwise impregnation and evaluated for CO2 methanation. The preparation procedure preserved the crystalline structure of the zeolite and enabled effective deposition of the active phase without additional shaping. Increasing the Ni loading from 5 to 10 wt% enhanced catalytic performance, while Rh and Ru exhibited distinct loading-dependent effects: 0.3 wt% Rh2O3 was sufficient to achieve near-maximum performance within the investigated Rh loading range, whereas the activity of Ru-promoted catalysts increased progressively with RuO2 loading. The promoted Ni-based catalysts achieved CO2 conversions of up to 82.5%, with CH4 selectivities reaching 86% for Ni–Rh/13X and 85% for Ni–Ru/13X at 450–500 °C. Combined SEM–EDS, H2-TPR, CO2-TPD, and Raman analyses revealed distinct promoter effects: Rh was associated with a more homogeneous spatial distribution of the Ni-containing phase and a redistribution of basic sites, whereas Ru more strongly enhanced catalyst reducibility. The observed CO formation was consistent with the involvement of the RWGS reaction followed by CO hydrogenation; however, an associative pathway involving the hydrogenation of adsorbed CO2-derived species cannot be excluded. Overall, the results demonstrate that low Rh and Ru loadings can effectively modify the physicochemical and catalytic properties of Ni/13X, providing a simple approach to the development of CO2 methanation catalysts based on commercially available zeolite granules.
Solar-driven CO₂ reduction technologies face unique challenges when transitioning from laboratory to prototype scale. Within the European Union-funded SunCoChem project, a photoelectrochemical reactor was designed and validated for CO₂ conversion to a CO-rich syngas stream, scalable to 2400 cm², for subsequent upgrading in a hydroformylation unit. Beyond selectivity, ensuring process durability is critical for economic viability, yet degradation pathways are difficult to identify at the prototype scale, where conventional gas-product analysis provides only delayed and indirect information. Here we couple operando electrochemical impedance spectroscopy (EIS) with distribution of relaxation times (DRT) analysis on a 120 cm² BiVO₄-photoanode/Cu₂O–SnO₂-cathode device, and combine it with targeted stress testing, to resolve and monitor failure modes in real time. The prototype sustained CO-dominant operation for over 200 h at 6.1 mA cm⁻², with average Faradaic efficiencies of ∼81% to CO and ∼10% to H₂ and a solar-to-chemical efficiency of 4.3–5.0%. DRT resolved distinct impedance signatures associated with gas-chamber overpressure, GDE flooding and photoanode degradation, providing a non-invasive diagnostic framework. We discuss the current technological bottlenecks and outline strategies for further optimization and scale-up.
Foam-assisted CO2 storage has the potential to enhance CO2 mobility control and improve storage security in saline aquifers. However, its effectiveness depends on the ability of surfactant formulations to stabilize CO2-brine interfaces under high-pressure conditions with varying salinities typical of saline formations. In this study, the interfacial and bulk foam performances of three field-relevant surfactant formulations, namely anionic (sulfonate-based, SUR-402), cationic switchable (amine-based, D-TTM) and viscoelastic-forming (quaternary ammonium-based, FTS-20) were systematically evaluated at low surfactant concentrations under aquifer-relevant conditions. Experiments were conducted at 60 °C and 8.6 – 13.8 MPa using low-salinity (38.44 g/L) and high-salinity (241.67 g/L) brines. The apparent interfacial critical micelle concentration (CMCIFT) was identified from the CO2-brine interfacial tension (IFT)-concentration responses and subsequently employed to define surfactant dosages (0.10 – 0.25 wt%) for foam stability measurements. The results revealed a pronounced salinity dependence on surfactant performances. At low salinity, the anionic formulation achieved the lowest IFT (4.5 mN/m) and longest foam half-life at 0.10 wt% (132.8 min). Under high-salinity conditions, however, its performance deteriorated markedly. In contrast, the switchable amine formulation maintained low IFT values (≈5.3 mN/m) and exhibited long foam half-lives (>300 min at 0.25 wt%), reflecting strong salinity tolerance. The viscoelastic system produced robust foam persistent across both salinity regimes, with maximum half-life exceeding 400 min at 0.25 wt%. Importantly, a clear decoupling was observed between equilibrium IFT reduction and long-term foam stability. These findings indicate that dynamic interfacial film properties, dictated by surfactant chemistry and brine composition, control foam persistence under saline environments. This study provides practical guidance for surfactant selection by showing that optimal foam stabilization for CO2 storage is strongly formation-specific and governed by salinity-dependent stabilization pathways. These findings establish a comparative screening framework for surfactant selection under reservoir-relevant conditions and provide a basis for subsequent porous media validation.
In recent years, the substantial emission of carbon dioxide (CO2) has caused increasingly severe environmental issues. In response, policies related to carbon neutrality and carbon emission reduction have been rolled out. To achieve these goals, the efficient capture of CO2 is essential. This work systematically elucidated the gas-liquid two-phase counter-current mass transfer mechanism for an efficient CO2 absorption process using a curved tube-in-tube reactor (TiTR), which has a wide gas-liquid contact area and a new reactor structure. The variation of CO2 absorption efficiency and the overall gas-liquid volumetric mass transfer coefficient (kLa) under different experimental conditions, including curvature diameter, pitch, and liquid flow rate, was systematically examined. Through the optimization of experimental conditions, the enhancement factor of kLa, which was defined as the ratio of kLa of the curved TiTR to that of the straight TiTR, reached 1.35, and kLa was up to 0.97 s−1. In addition, the trade-off between mass transfer enhancement and energy consumption in the CO2 absorption enhancement process within TiTRs with different geometries was evaluated. Finally, on the basis of the experimental data, an empirical equation correlating kLa with experimental parameters was further proposed. This equation can be used to predict the gas-liquid mass transfer in TiTRs.
CO2 flooding has emerged as a key tertiary oil recovery technology, offering dual benefits of enhanced hydrocarbon production and CO2 geological storage while reducing greenhouse gas emissions. This technology demonstrates significant value for energy development and environmental protection, positioning it as a strategic solution for the low-carbon development of the petroleum industry. Nevertheless, achieving CO2 miscible flooding remains challenging in low-pressure reservoirs. To address this issue, a series of molecular dynamics models were established in this study. First, a CO2–n-decane model was constructed to calculate the minimum miscibility pressure (MMP) of the system. Subsequently, three surfactants were incorporated into the model to identify the optimal surfactant based on their miscibility reduction capability. Finally, pure CO2 flooding and CO2–optimized surfactant hybrid flooding models were developed, establishing a micro–macro correlation to elucidate the underlying oil displacement mechanisms. Simulation results revealed distinct pressure-dependent miscibility behavior in the CO2–n-decane system. Increasing pressure induced n-decane phase expansion and a linear reduction in interfacial tension. The calculated minimum miscibility pressure showed good agreement with literature values. All three surfactants reduced the MMP by more than 10%, with dodecyl peracetylglucoside (FADG) exhibiting the highest reduction of 16.79%. Mechanistically, the surfactants promoted CO2 dissolution mainly through preferential adsorption at the CO2–n-decane interface, which weakens local n-decane cohesion in the interfacial/transition region while strengthening CO2–n-decane interactions and accelerating interfacial mass transfer. For FADG in particular, the oxygen-rich acetylated headgroup provides multiple CO2-philic sites, enabling denser interfacial packing and stronger interfacial free-energy reduction, which is consistent with its steepest IFT–pressure slope and the largest MMP reduction. In engineering practice, surfactants are co-injected with CO2; accordingly, in the displacement simulations surfactants were initially dispersed in the CO2 phase, whereas in the miscibility-screening model surfactants were initialized at the CO2/oil interface to represent their rapid interfacial partitioning under amphiphilic driving forces. Displacement simulations further demonstrated a synergistic effect between pressure and surfactant addition. Although increasing pressure improved oil recovery, its effect became saturated after achieving miscibility. The addition of FADG enhanced displacement efficiency by 7.094% at 345 K and 11.289 MPa, primarily by facilitating the detachment of residual oil. Displacement efficiency showed a positive correlation with FADG concentration in the range of 0–0.966 wt%; at higher concentrations, the improvement plateaued and slightly decreased because surfactant self-association reduced the number of free molecules available for interfacial adsorption.
Direct aqueous carbonation of olivine is a promising route for permanent CO₂ mineralization, but its conversion efficiency remains constrained by silica passivation, incomplete lattice activation, and inefficient utilization of extracted magnesium. Conventional pretreatment strategies often seek to maximize mineral surface area; however, the relationship between physical activation and carbonation efficiency remains ambiguous. Here, we systematically decouple surface-area generation from carbonation reactivity by comparing DI-water, alkaline (NaOH, KOH), inorganic-acid (H₂SO₄, HNO₃), organic-chelator (citric, ascorbic, oxalic), and alkaline-silicate (Na₂SiO₃) pretreatments. The results reveal that high porosity alone does not guarantee CO₂ uptake from the washed solid residues. Strong inorganic-acid pretreatments generated the highest surface area (up to 27.12 m² g⁻¹), but the corresponding washed solids produced low CO₂ uptake efficiency (4.6%), consistent with extensive Mg removal from the solid residue and formation of chemically unfavorable reacted interfaces. Organic acids promoted ligand-controlled Mg²⁺ mobilization; in particular, oxalic acid diverted Mg into crystalline glushinskite (MgC₂O₄·2H₂O), while citric/ascorbic systems are more consistent with soluble complexation, washing loss, and/or mineral-derived surface alteration. Strong bases largely preserved the crystalline forsterite framework and released little Mg²⁺. By contrast, Na₂SiO₃ pretreatment produced a sodium-incorporated Mg-Si interfacial structure that retained Mg within the solid matrix while providing an alkaline environment favorable for subsequent carbonate formation. After controlled carbonation, the Na₂SiO₃ pathway produced crystalline magnesium carbonate and achieved the highest CO₂ uptake efficiency (39.5%). These findings demonstrate that Mg fate, preservation of intrinsic alkalinity, and interfacial reaction chemistry—rather than BET surface area alone—govern carbonation efficiency. The study provides a mechanistic basis for designing chemically buffered silicate activation strategies for scalable CO₂ mineralization and utilization.
Carbon dioxide (CO2) is a thermodynamically stable yet versatile C1 feedstock whose reactivity can be accessed through catalytic design. Recent advances in organocatalysis have shifted CO2 conversion from a focus on activation feasibility to control over reactive intermediates and selectivity. Visible-light photoredox catalysis and radical relay strategies enable single-electron activation pathways, allowing C–H carboxylation, cascade difunctionalization, radical anion processes, and transient CO2-mediated protection under mild, metal-free conditions. Beyond activation through energetic input, control of noncovalent interactions, confined catalytic environments, and cooperative Lewis acid–base systems enable stereocontrolled CO2 incorporation. From hydrogen-bond-driven enantioselective cyclizations and chalcogen-bond activation to stereodivergent photocatalysis, substrate-controlled transformations, and enantioselective carbon isotope exchange, these developments demonstrate controlled CO2 incorporation across diverse reaction pathways and modes of selectivity. This review summarizes recent advances in organocatalytic CO2 utilization, emphasizing the integration of activation modes, control over reactive intermediates and selectivity, and sustainable reaction design.
The increasing concentration of atmospheric CO₂ has intensified the need for sustainable carbon management strategies. This review explores the emerging field of CO₂ utilization, emphasizing the conversion of CO₂ into value-added products (CO₂-to-X) and integrating the CO₂-to-carbon pathway. We provide a comprehensive analysis of chemical and electrochemical conversion routes, highlighting the thermodynamic, kinetic, and technological challenges associated with each approach. The CO₂-to-X pathways encompass fuels, chemicals, polymers, and materials, demonstrating the potential to simultaneously mitigate emissions and generate economic value. Particular attention is given to the CO₂-to-carbon pathway, including the production of solid carbon materials such as graphite, carbon nanotubes, and graphene via the Bosch process, which offer high-value applications in energy storage, construction, and advanced manufacturing. By synthesizing recent advances and identifying gaps in the literature, this paper provides a roadmap for researchers and industry practitioners aiming to transform CO₂ from an environmental liability into a resource. The study underscores the dual potential of CO₂ utilization: reducing greenhouse gas emissions while fostering innovative pathways for carbon-based products, thereby contributing to a circular carbon economy.
Potassium (K) has been widely employed as an alkali promoter for Fe-based catalysts in the reverse water gas shift (RWGS) reaction, Fischer-Trospch synthesis (FTS) and the integration of RWGS and FTS for direct CO2 hydrogenation to higher hydrocarbons, commonly referred to as the CO2-FTS process. K is recognized as both a structural promoter of the Fe phase and an electronic promoter that modifies the adsorption and activation behavior of reactants on the catalyst surface. However, its role in reaction pathways and the effect of K loading in each reaction remains largely unexplored. In this study, a series of K-promoted carbon-supported Fe-based catalysts was prepared to investigate the effect of K/Fe molar ratios from 0.02 to 0.5 on the RWGS and FTS reactions in a fixed-bed reactor at 300 °C, 11 bar, H2/CO2/Ar=3/1/1, 1000–375000 mL·gcat−1·h−1. Quasi in situ Mössbauer spectroscopy shows that sufficient K promotion (K/Fe ≥ 0.1) on carbon-supported Fe-based catalysts led to complete carburization following a reduction-carburization activation procedure. The resulting Fe carbides remained stable after both RWGS and FTS conditions, suggesting that they are responsible for catalyzing both reactions. This finding contrasts with literature reports that attribute RWGS and FTS activity to Fe oxides and Fe carbides, respectively. Increasing the K/Fe ratio progressively suppressed CO2 methanation as a primary reaction, ultimately rendering primary methanation insignificant and leaving RWGS as the only primary reaction. Both RWGS and FTS activities reached their optimum at a K/Fe ratio of 0.1. However, a higher K/Fe ratio led to higher CO selectivity in the RWGS reaction, whereas an optimal K/Fe ratio of 0.1 was found for FTS to promote the production of higher hydrocarbons.
This paper presents a cost analysis of Synthetic Natural Gas (SNG) produced by methanation of green hydrogen and carbon dioxide (CO2) in the Australian context. A range of CO2 sources, including biogas, direct air capture (DAC), and industry point sources, is considered. With zero-cost electricity, SNG can be produced for 21–32 AUD/GJ, at a premium of 7–22 AUD/GJ over hydrogen. The important role of technology learning and scale is also highlighted, particularly when biogas is used as a CO2 source. A key contributor to the cost premium of SNG over hydrogen is the need to produce approximately 28% more hydrogen, whose heating value is converted to heat during methanation. The cost premium of SNG may be justified by its advantages, including compatibility with existing natural gas infrastructure, ease of storage and transport, and the potential for faster market integration.
This study investigates the influence of metal–support interaction (MSI) on the performance of Ni/MgAl₂O₄ catalysts for CO₂ methanation. Modulating MSI in NiMgAl₂O₄ is shown to be an effective approach to enhance catalytic activity and CH₄ selectivity. A series of 15 wt% Ni/MgAl₂O₄ catalysts were synthesized by varying the calcination temperature (300–1000 °C) to tailor Ni particle size, dispersion, Ni–Mg–Al oxide formation, and active site characteristics. Catalysts were benchmarked against Ni/MgO and Ni/Al₂O₃ calcined at 850 °C. Textural analysis (N₂ adsorption–desorption) revealed a decline in surface area with increasing calcination temperature but an optimal texture at 850 °C. Characterization by H₂-TPR, XRD, UV–vis, TEM, and XPS confirmed progressive MSI strengthening, the development of Ni–Mg–Al mixed oxides and NiAl₂O₄ phases, smaller NiO crystallites, and partial Ni incorporation into the MgAl₂O₄ lattice at higher temperatures. In-situ DRIFTS identified temperature-dependent surface intermediates during CO₂ methanation over NiMgAl850: carbonate/bicarbonate species dominated below 200 °C, while formate and adsorbed CO correlated with CH₄ formation above 200 °C. Among the series, NiMgAl850 exhibited the smallest NiO crystallite size (∼5.6 nm), well-balanced MSI, and optimal surface basicity, delivering the highest CO₂ conversion and CH₄ selectivity. Post-reaction XRD, Raman, and spent-catalyst analyses confirmed minimal sintering, coking, and phase transformation (400–550 °C). Compared with Ni/MgO and Ni/Al₂O₃, the Ni–MgAl₂O₄ interface provides a balanced MSI environment, avoiding excessively strong Ni–MgO or NiAl₂O₄ interactions, thus ensuring stable and active CO₂ methanation performance.
Background The continuous rise in atmospheric carbon dioxide (CO₂) levels and increasing global energy demand have intensified the need for sustainable technologies that simultaneously valorize CO₂ and generate clean fuels. Among solar-driven approaches, photocatalytic CO₂ utilization offers a promising pathway for converting CO₂ into value-added chemicals while coupling with hydrogen (H₂) evolution to enhance overall solar energy conversion efficiency. Layered double hydroxides (LDHs) have emerged as attractive photocatalysts owing to their two-dimensional layered architecture, abundant surface hydroxyl groups, and tunable multi-metal composition, enabling precise modulation of electronic structures, band alignment, and active catalytic sites for efficient multi-electron redox reactions. Methods This review critically summarizes recent advances in LDH-based photocatalysts for photocatalytic CO₂ utilization and H₂ evolution, including pristine LDHs, defect-engineered LDHs, heterojunctions, hybrid nanocomposites, and LDH-derived mixed metal oxides (MMOs). Particular emphasis is placed on the influence of compositional engineering and interface design on light harvesting, charge carrier dynamics, CO₂ activation, product selectivity, and photocatalytic performance. Significant findings Structural and compositional engineering significantly enhances the visible-light response, charge separation, and interfacial charge transfer of LDH-based photocatalysts. Hybrid architectures and LDH-derived MMOs further improve catalytic efficiency by increasing active reaction sites and strengthening interfacial interactions, thereby promoting efficient CO₂ conversion into valuable solar fuels and chemicals while simultaneously facilitating sustainable H₂ production. These advances highlight LDHs as highly promising platforms for integrated solar-driven CO₂ utilization and renewable energy generation.
The Reverse Boudouard Reaction (RBR) is a key chemical process with significant industrial relevance in various transformations such as gasification, coke removal, and smelting in blast furnaces. Although it is a highly endothermic reaction favored at elevated temperatures, RBR offers a promising pathway not only for mitigating atmospheric CO₂ emissions and producing clean fuels but also for waste/biomass valorization. Several factors can influence the rate of RBR. Typically, these factors are the carbon characteristics, oxygen transfer mechanism, the type of catalyst and its underlying mechanism and the reaction environment. Carbon with lower graphitic character and a high defect density is more easily gasified. In addition, the presence of dopants and oxygenated groups enhances the CO2 gasification. For non-catalytic systems, RBR takes place via direct CO2 dissociation at carbon surface, hence the reaction rate remains low. In the presence of alkali and alkaline earth metal oxides, in particular, K2O, Na2O, CaO and MgO are the most active catalysts for RBR owing to their ability to adsorb and activate CO2. In addition, Fe and Ni can catalyze RBR assigned to their ability to dissociate CO2 and bind with oxygenated species resulting from CO2 dissociation and hence mediate oxygen transfer through redox cycles. Mixed system comprised of transition metals/alkali or alkaline earth metal oxide can provide enhanced reactivity attributed to their dual function of CO₂ activation and oxygen transfer. In systems containing ceria, CO₂ can be activated at oxygen vacancies, producing CO and replenishing lattice oxygen, which is subsequently transferred to the carbon surface, oxidizing it to CO and regenerate vacant sites in a redox cycle. In metal-supported ceria, the metal phase facilitates CO₂ adsorption and dissociation, while the oxide support enhances oxygen mobility and storage capacity, enabling continuous oxygen supply to the carbon. Despite being investigated in diverse contexts, the reaction and its applications were not comprehensively reviewed or emphasized in previous studies. In this review, we highlighted the fundamental aspects of the RBR as a universal approach for CO₂ activation and valorization, which is mainly influenced by carbon structure, catalyst functionality, and oxygen transfer mechanisms. In addition, its practical applications were highlighted with special reference to catalyst regeneration, biomass valorization, and electricity generation via direct carbon fuel cells. Although, RBR is the main stream in these applications, however, they differ in terms of carbon characteristics, catalyst type and operating environment.
Electrochemical CO2 reduction has attracted considerable research interest as a pathway to convert CO2 into value-added multicarbon products. Cu is a key catalyst for multicarbon-product formation, and its selectivity is strongly affected by its microstructure. However, the effect of the gas environment during electrodeposition on Cu growth and subsequent CO2 reduction performance remains poorly understood. Here, Cu catalysts were directly grown on a gas diffusion layer (GDL) in a flow-cell-based electrodeposition system while either CO2 or Ar was supplied to the backside of the GDL, allowing the gaseous growth environment to be varied during deposition. The electrodes prepared under backside CO2 supply exhibited finer surface features, and the representative Cu-gCO2−20 electrode showed a more highly subdivided crystallographic microstructure than the corresponding Ar-prepared electrode. These structural differences were associated with enhanced C2+ selectivity during subsequent CO2 reduction. Under representative operating conditions, the optimized electrode fabricated under CO2-supplied conditions achieved a C2+ Faradaic efficiency of approximately 70% and an FEC2+/FEC1 ratio of 5.5, compared with 2.7 for the corresponding Ar-prepared electrode. These findings highlight backside gas supply as an additional electrodeposition parameter for promoting the selective conversion and reuse of CO2 into multicarbon products, including ethylene and ethanol.
Carbon dioxide capture, utilization, and storage–enhanced oil recovery (CCUS–EOR) depends on the progressive development of CO₂–oil miscibility, yet the pressure-controlled transition from interfacial mass transfer to porous-media miscible-zone propagation remains difficult to quantify. In this study, X-ray computed tomography (CT) was combined with a time-series dual-energy CT material decomposition fusion algorithm (TDEMDF) to visualize CO₂–oil contact, quantify density redistribution, and reconstruct saturation during direct-contact and core-flooding experiments. The interfacial-tension-extrapolated minimum miscibility pressure (MMP) was 14.21 MPa; however, CT observations showed that MMP marks a mechanism transition rather than complete density equilibration. A miscible zone appeared at 9 MPa and evolved through three stages: CO₂ dissolution dominated at 9–14 MPa, oil-component extraction dominated from the MMP to the density-equilibrium threshold pressure (PDE) of 18.62 MPa, and miscible-zone expansion dominated above PDE. Although complete CT-density parity between the CO₂-rich and oil-rich regions would require an extrapolated pressure of approximately 36.03 MPa, density-difference reduction became much less pressure-sensitive above 18.62 MPa. A density-difference-normalized apparent miscibility index coupled with Tsallis entropy revealed stepwise miscibility enhancement. Core-flooding results further showed that pore structure restricts CO₂–oil contact, lowering the peak Tsallis entropy from 2.92 in direct-contact experiments to 2.64 in porous media. Compared with the conventional method, TDEMDF reduced MAE from 16.41 to 6.23, improving saturation-estimation performance by 50.2%. These results demonstrate that CO₂–oil miscibility continues to evolve beyond the MMP and provide a CT-based framework for pressure optimization, miscible-zone monitoring, and saturation reconstruction in CCUS–EOR.
Designing efficient and selective electrocatalysts for CO2 reduction remains a central challenge in sustainable chemistry. In this work, we present a comparative theoretical investigation of carborane-based single-site clusters, MC2B9H11 (M = Cu, Ir), for the CO2 reduction reaction (CO2RR) using detailed electronic structure analysis and Gibbs free energy profiling. Key electronic descriptors — including frontier molecular orbitals, spin density, density of states, and electrostatic potential maps — reveal two fundamentally distinct catalytic regimes dictated by the identity of the metal center. Both CuC2B9H11 and IrC2B9H11 efficiently catalyze CO2 reduction, with CO identified as the most thermodynamically favorable product on both surfaces. CuC2B9H11 further promotes selective formation of oxygenated products such as formaldehyde and methanol through stabilized intermediate pathways. In contrast, IrC2B9H11 primarily favors CO evolution, with suppressed selectivity toward deeper hydrogenation and alternative reduction products. Solvent effects further differentiate the active metal center catalytic behavior. For the Ir system, intermediates are uniformly stabilized, leading to a nearly constant downward shift in free energies with minimal perturbation of relative reaction energetics, consistent with non-specific electrostatic stabilization. In contrast, the Cu system displays non-uniform solvation-induced reshaping of the potential energy surface, where polar intermediates are preferentially stabilized. This selective stabilization alters relative energetics and induces a solvent-driven shift in the preferred configuration of the *CHOH intermediate. Such behavior reflects a higher sensitivity of the Cu-centered electronic structure to the dielectric environment, arising from its more localized charge distribution and weaker metal–ligand delocalization.
Industrial activities have led to increasing CO₂ emissions, making the development of efficient conversion pathways essential. In this study, density functional theory (DFT) calculations were employed to explore the effect of Cu doping on the adsorption, activation, and hydrogenation of CO₂ over NHC-Cu-H functionalized ZIF-90 (denoted as NHC-Cu-H/ZIF-90). Comparative analysis of NHC-Cu-H/ZIF-90 and NHC-Cu-H/Cu-doped ZIF-90 was carried out to clarify the effect of Cu doping on the catalyst’s electronic structure and reaction pathway. DFT-based electronic structure analysis revealed that Cu doping in the ZIF-90 framework modifies the electronic environment of the NHC-Cu-H active site, increasing Cu-H bond polarization and strengthening Cu-H orbital overlap. Mechanistic analysis revealed that for both catalytic systems, the carboxyl pathway is kinetically unfavorable, and that CO₂ hydrogenation preferentially proceeds via the formate pathway. Along this pathway, the concerted cleavage of the C-O and. O-H bonds in the CH₂OHOH intermediate, leading to the formation of HCHO and H₂O, were identified as the rate-determining step for both catalysts, with activation energy barriers of 1.63 and 1.70 eV for NHC-Cu-H/Cu-doped ZIF-90 and NHC-Cu-H/ZIF-90, respectively. Energetic span analysis further showed that Cu doping reduces the energetic span from 0.77 to 0.63 eV, leading to an estimated increase in the turnover frequency (TOF) from 0.60 to 143 s⁻¹ , corresponding to an enhancement of more than two orders of magnitude in catalytic activity. Furthermore, the results showed that Cu doping facilitates the heterolytic dissociation of H₂ and improves hydrogen activation. Kinetic analysis revealed that Cu doping decreases the activation free energy barrier (ΔG‡) for hydride transfer to CO₂ from 0.09 to 0.05 eV, thereby increasing the corresponding rate constant. In contrast, Cu doping slightly increases ΔG‡ for hydride transfer to HCOOH and HCHO, leading to lower rate constants for these subsequent hydrogenation steps. Nevertheless, Cu doping improves the overall catalytic behavior by facilitating H₂ activation, promoting the initial hydrogenation of CO₂, and slightly lowering the activation energy barrier of the rate-determining step.
CO2 binding organic liquids (CO2BOLs) are a promising class of water-lean solvents for CO2 capture, with improved performance compared to traditional aqueous amines. This study systematically examines the role of hydroxy compounds and their molecular features on CO2 chemisorption in binary 1,8-diazabicyclo[5.4.0]undec-7-ene-based CO2BOLs using a combined density functional theory (DFT) and experimental approach. A series of hydroxy compounds from linear and branched alkanols, polyols, and ether-functionalized alcohols are evaluated to elucidate structure–property relationships governing CO2 binding, reaction energetics, and absorption performance. DFT-based topological and energetic analyses reveal that CO2 uptake is controlled by a balance between strong DBU–hydroxy hydrogen bonding and weaker, reversible CO2–oxygen interactions. Experimental measurements of CO2 loading and absorption enthalpy confirm a pronounced thermodynamic–kinetic trade-off, where polyols exhibit strong CO2 binding but suffer from high activation barriers and regeneration penalties, whereas linear alkanols favor faster kinetics with weaker thermodynamic driving forces. Branched alkanols and ether-containing alcohols provide an optimal intermediate regime, achieving higher CO2 loadings with moderate absorption enthalpies. The combined experimental–computational framework presented here provides mechanistic insight and practical guidelines for the rational design of next-generation CO2BOLs, advancing the development of efficient and regenerable water-lean solvents for CO2 capture.
This work proposes a new conceptual design for the direct conversion of CO2 and H2 to syncrude, which consists of three reactors in series with intermediate water removal and H2 feeding. The first reactor is a low-temperature Fischer–Tropsch (FT) reactor with a cobalt catalyst using syngas as a feed, followed by two high-temperature FT reactors with an iron catalyst simultaneously active for both Reverse Water Gas Shift (RWGS) and FT reactions, fed with CO2 containing 1% inert. The process design incorporates tail gas recycling to improve CO2 conversion and partial oxidation to reform light hydrocarbons and produce syngas. The process flowsheet was developed in Aspen Plus using a custom kinetic model that accounts for the variable chain growth probability distribution (α) along the reactor length. The process was optimized using the Particle Swarm Optimization (PSO) algorithm implemented in Python. The objective function of the optimization model is to minimize the total annualized cost per kilogram of product produced. The optimum design, with a minimum selling price of 1.68$kg-1 excluding the cost of captured CO2, exhibits a high tail-gas recycle ratio and a carbon efficiency of about 95%. A sensitivity analysis is performed by varying the electricity price and the capital investment factor by ± 40% to investigate the impact on the design parameters and the objective function. The majority of the total cost consists of the electricity required to produce green hydrogen and capital expenditures related to electrolyzer investment (about 74% of total capital investment).
