CO2 Capture and Utilization Editorial

A bimetallic (Cu-Zn) doping platform for enhancement of CO2 capture and separation by a cost-effective biomass-based activated carbon

This study presents an efficient method for CO2 capture and separation using low-cost corncob-based activated carbon/metal nanoparticles (MNPs/AC) composites. Initially, the optimization of AC synthesis was conducted by varying activating agent/precursor ratios and activation temperature. Subsequently, the highly porous AC was modified using a polyol method with a single and binary mixture of Cu2+ and Zn2+ metals. The raw AC, Cu/AC, Zn/AC, and Cu-Zn/AC composites were extensively characterized through BET, FESEM-EDX, FT-IR, TGA, and Boehm's titration analyses. Gas adsorption results revealed that the bimetallic composite sample, Cu-Zn/AC, demonstrated the highest CO2 capture capacity of 5.41 mmol/g compared to the parent AC (3.25 mmol/g) as well as the single metal-doped ACs, Cu/AC (4.19 mmol/g) and Zn/AC (4.38 mmol/g) at 1 bar and 25 °C due to stronger synergistic effects. In addition, the selectivity of CO2/N2 and CO2/CH4 was also studied for samples using the Ideal Adsorption Solution Theory (IAST) at 25 °C and 1 bar. Among all samples, Cu-Zn/AC showed excellent selectivity towards CO2/N2 and CO2/CH4 with values of 65 and 16, respectively. The higher selectivity for metal-doped samples compared to the pristine AC is due to a stronger interaction between the introduced MNPs and CO2 molecules, as indicated by the higher isosteric heat of CO2 adsorption. These results suggest that the bimetallic (Cu-Zn) doped AC is an effective and low-cost adsorbent for natural gas upgrading and flue gas CO2 capture.

A review of metal-organic frameworks and polymers in mixed matrix membranes for CO2 capture

Polymeric membranes offer an appealing solution for sustainable CO2 capture, with potential for large-scale deployment. However, balancing high permeability and selectivity is an inherent challenge for pristine membranes. To address this challenge, the development of mixed matrix membranes (MMMs) is a promising strategy. MMMs are obtained by carefully integrating porous nano-fillers into polymeric matrices, enabling the simultaneous enhancement of selectivity and permeability. In particular, metal-organic frameworks (MOFs) have gained recognition as MMM fillers for CO2 capture. Here, a review of the current state, recent advancements, and challenges in the fabrication and engineering of MMMs with MOFs for selective CO2 capture is proposed. Key considerations and promising research directions to fully exploit the gas separation potential of MOF-based MMMs in CO2 capture applications are highlighted.

Recent advances in CO2 capture and mineralization using layered double hydroxide-based materials: A review

The continuous release of substantial amounts of carbon dioxide (CO2) to the atmosphere has resulted in numerous severe adverse effects. Several materials have been synthesized and utilized for CO2 capture. One class of such materials is layered double hydroxides (LDHs), which have emerged as promising materials for CO2 capture due to their tunable properties, high surface area, and excellent CO2 adsorption capabilities. Although there are some review articles on CO2 capture and conversion using various materials, there is still a notable lack of thorough reviews focusing on the utilization of LDH-based materials for CO2 capture. Additionally, the field of CO2 capture and mineralization using LDH-based materials is rapidly evolving, necessitating up-to-date comprehensive reviews to analyze, evaluate, and condense the dispersed information found in recently published research articles. Accordingly, this review article provides a comprehensive overview of recent advancements in CO2 capture using LDH-based materials. After briefly introducing the topic, different synthesis protocols of LDH-based materials are briefly reviewed. Then, CO2 capture using LDHs, calcined LDHs, impregnated LDHs, composites containing LDHs, amine functionalized LDHs, and during steam methane reforming, are thoroughly analyzed and discussed. Additionally, the effects of synthesis method and post treatment of LDH-based materials on CO2 capture, effect of modification and functionalization on LDHs, and the effects of various process conditions including temperature, pressure, water vapor, and gas composition on the performance of CO2 capture by LDH-based materials are reviewed. Limitations, challenges, obstacles, and remaining knowledge gaps are highlighted, and future research works to address them are proposed.

An Atomistic View on the Mechanism of Diatom Peptide-Guided Biomimetic Silica Formation

Deciphering nature's remarkable way of encoding functions in its biominerals holds the potential to enable the rational development of nature-inspired materials with tailored properties. However, the complex processes that convert solution-state precursors into solid biomaterials remain largely unknown. In this study, an unconventional approach is presented to characterize these precursors for the diatom-derived peptides R5 and synthetic Silaffin-1A1 (synSil-1A1). These molecules can form defined supramolecular assemblies in solution, which act as templates for solid silica structures. Using a tailored structural biology toolbox, the structure-function relationships of these self-assemblies are unveiled. NMR-derived constraints are employed to enable a recently developed fractal-cluster formalism and then reveal the architecture of the peptide assemblies in atomistic detail. Finally, by monitoring the self-assembly activities during silica formation at simultaneous high temporal and residue resolution using real-time spectroscopy, the mechanism is elucidated underlying template-driven silica formation. Thus, it is demonstrated how to exercise morphology control over bioinorganic solids by manipulating the template architectures. It is found that the morphology of the templates is translated into the shape of bioinorganic particles via a mechanism that includes silica nucleation on the solution-state complexes' surfaces followed by complete surface coating and particle precipitation.

Models for Decarbonization in the Chemical Industry

Various technologies and strategies have been proposed to decarbonize the chemical industry. Assessing the decarbonization, environmental, and economic implications of these technologies and strategies is critical to identifying pathways to a more sustainable industrial future. This study reviews recent advancements and integration of systems analysis models, including process analysis, material flow analysis, life cycle assessment, techno-economic analysis, and machine learning. These models are categorized based on analytical methods and application scales (i.e., micro-, meso-, and macroscale) for promising decarbonization technologies (e.g., carbon capture, storage, and utilization, biomass feedstock, and electrification) and circular economy strategies. Incorporating forward-looking, data-driven approaches into existing models allows for optimizing complex industrial systems and assessing future impacts. Although advances in industrial ecology-, economic-, and planetary boundary-based modeling support a more holistic systems-level assessment, more efforts are needed to consider impacts on ecosystems. Effective applications of these advanced, integrated models require cross-disciplinary collaborations across chemical engineering, industrial ecology, and economics.

Integrated CO2 capture and reduction catalysis: Role of γ-Al2O3 support, unique state of potassium and synergy with copper

Carbon dioxide capture and reduction (CCR) process emerges as an efficient catalytic strategy for CO2 capture and conversion to valuable chemicals. K-promoted Cu/Al2O3 catalysts exhibited promising CO2 capture efficiency and highly selective conversion to syngas (CO + H2). The dynamic nature of the Cu-K system at reaction conditions complicates the identification of the catalytically active phase and surface sites. The present work aims at more precise understanding of the roles of the potassium and copper and the contribution of the metal oxide support. While γ-Al2O3 guarantees high dispersion and destabilisation of the potassium phase, potassium and copper act synergistically to remove CO2 from diluted streams and promote fast regeneration of the active phase for CO2 capture releasing CO while passing H2. A temperature of 350℃ is found necessary to activate H2 dissociation and generate the active sites for CO2 capture. The effects of synthesis parameters on the CCR activity are also described by combination of ex-situ characterisation of the materials and catalytic testing.

Accelerated Discovery of Metal-Organic Frameworks for CO2 Capture by Artificial Intelligence

The existence of a very large number of porous materials is a great opportunity to develop innovative technologies for carbon dioxide (CO2) capture to address the climate change problem. On the other hand, identifying the most promising adsorbent and membrane candidates using iterative experimental testing and brute-force computer simulations is very challenging due to the enormous number and variety of porous materials. Artificial intelligence (AI) has recently been integrated into molecular modeling of porous materials, specifically metal-organic frameworks (MOFs), to accelerate the design and discovery of high-performing adsorbents and membranes for CO2 adsorption and separation. In this perspective, we highlight the pioneering works in which AI, molecular simulations, and experiments have been combined to produce exceptional MOFs and MOF-based composites that outperform traditional porous materials in CO2 capture. We outline the future directions by discussing the current opportunities and challenges in the field of harnessing experiments, theory, and AI for accelerated discovery of porous materials for CO2 capture.

Boosting CO2 Conversion by Synergy of Lead-Free Perovskite Cs2SnCl6 and Plasma with H2O

Although dielectric barrier discharge (DBD) plasma is a promising technique for CO2 conversion, realizing CO2-to-alcohol is still challenging via the use of H2O. Herein, for the first time, efficient CO2 conversion was achieved via the synergism between the Cs2SnCl6 photocatalyst and DBD plasma assisted by H2O. The CO2 conversion ratio of plasma photocatalysis was 6.5% higher than that of only the plasma and photocatalysis, implying that the synergism of plasma catalysis and photocatalysis was achieved. Furthermore, the DBD plasma assisted by the Cs2SnCl6 photocatalyst could convert CO2 and H2O to CO and a small amount of methanol and ethanol. The CO2 conversion ratio was enhanced by 50.6% in the presence of H2O, which was attributed to the improvement of charge transfer due to the increased electrical conductivity of the photocatalyst surface during plasma discharge. This work provides a new idea for developing an efficient system 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.

A Robust Framework for Generating Adsorption Isotherms to Screen Materials for Carbon Capture

To rank the performance of materials for a given carbon capture process, we rely on pure component isotherms from which we predict the mixture isotherms. For screening a large number of materials, we also increasingly rely on isotherms predicted from molecular simulations. In particular, for such screening studies, it is important that the procedures to generate the data are accurate, reliable, and robust. In this work, we develop an efficient and automated workflow for a meticulous sampling of pure component isotherms. The workflow was tested on a set of metal-organic frameworks (MOFs) and proved to be reliable given different guest molecules. We show that the coupling of our workflow with the Clausius-Clapeyron relation saves CPU time, yet enables us to accurately predict pure component isotherms at the temperatures of interest, starting from a reference isotherm at a given temperature. We also show that one can accurately predict the CO₂ and N₂ mixture isotherms using ideal adsorbed solution theory (IAST). In particular, we show that IAST is a more reliable numerical tool to predict binary adsorption uptakes for a range of pressures, temperatures, and compositions, as it does not rely on the fitting of experimental data, which typically needs to be done with analytical models such as dual-site Langmuir (DSL). This makes IAST a more suitable and general technique to bridge the gap between adsorption (raw) data and process modeling. To demonstrate this point, we show that the ranking of materials, for a standard three-step temperature swing adsorption (TSA) process, can be significantly different depending on the thermodynamic method used to predict binary adsorption data. We show that, for the design of processes that capture CO₂ from low concentration (0.4%) streams, the commonly used methodology to predict mixture isotherms incorrectly assigns up to 33% of the materials as top-performing.

Highly selective CO2 photoreduction to CO on MOF-derived TiO2

Metal-Organic Framework (MOF)-derived TiO2, synthesised through the calcination of MIL-125-NH2, is investigated for its potential as a CO2 photoreduction catalyst. The effect of the reaction parameters: irradiance, temperature and partial pressure of water was investigated. Using a two-level design of experiments, we were able to evaluate the influence of each parameter and their potential interactions on the reaction products, specifically the production of CO and CH4. It was found that, for the explored range, the only statistically significant parameter is temperature, with an increase in temperature being correlated to enhanced production of both CO and CH4. Over the range of experimental settings explored, the MOF-derived TiO2 displays high selectivity towards CO (98%), with only a small amount of CH4 (2%) being produced. This is notable when compared to other state-of-the-art TiO2 based CO2 photoreduction catalysts, which often showcase lower selectivity. The MOF-derived TiO2 was found to have a peak production rate of 8.9 × 10-4 μmol cm-2 h-1 (2.6 μmol g-1 h-1) and 2.6 × 10-5 μmol cm-2 h-1 (0.10 μmol g-1 h-1) for CO and CH4, respectively. A comparison is made to commercial TiO2, P25 (Degussa), which was shown to have a similar activity towards CO production, 3.4 × 10-3 μmol cm-2 h-1 (5.9 μmol g-1 h-1), but a lower selectivity preference for CO (3 : 1 CH4 : CO) than the MOF-derived TiO2 material developed here. This paper showcases the potential for MIL-125-NH2 derived TiO2 to be further developed as a highly selective CO2 photoreduction catalyst for CO production.

Bioinspired and Bioderived Aqueous Electrocatalysis

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO2 reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices.

Modeling Differential Enthalpy of Absorption of CO2 with Piperazine as a Function of Temperature

Temperature-dependent correlations for equilibrium constants (ln K) and heat of absorption (ΔH_abs) of different reactions (i.e., deprotonation, double deprotonation, carbamate formation, protonated carbamate formation, dicarbamate formation) involved in the piperazine (PZ)/CO₂/H₂O system have been calculated using computational chemistry based ln K values input to the Gibbs-Helmholtz equation. This work also presents an extensive study of gaseous phase free energy and enthalpy for different reactions using composite (G3MP2B3, G3MP2, CBS-QB3, and G4MP2) and density functional theory [B3LYP/6-311++G(d,p)] methods. The explicit solvation shell (ESS) model and SM8T solvation free energy coupled with gaseous phase density functional theory calculations give temperature-dependent reaction equilibrium constants for different reactions. Calculated individual and overall reaction equilibrium constants and enthalpies of different reactions involved in CO₂ absorption in piperazine solution are compared against experimental data, where available, in the temperature range 273.15-373 K. Postcombustion CO₂ capture (PCC) is a temperature swing absorption-desorption process. The enthalpy of the solution directly correlates with the steam requirement of the amine regeneration step. Temperature-dependent correlations for ln K and ΔH_abs calculated using computational chemistry tools can help evaluate potential PCC solvents' thermodynamics and cost-efficiency. These correlations can also be employed in thermodynamic models (e.g., e-UNIQUAC, e-NRTL) to better understand postcombustion CO₂ capture solvent chemistry.

Photocatalytic Aqueous CO2 Reduction to CO and CH4 Sensitized by Ullazine Supramolecular Polymers

There has been rapid progress on the chemistry of supramolecular scaffolds that harness sunlight for aqueous photocatalytic production of hydrogen. However, great efforts are still needed to develop similar photosynthetic systems for the great challenge of CO₂ reduction especially if they avoid the use of nonabundant metals. This work investigates the synthesis of supramolecular polymers capable of sensitizing catalysts that require more negative potentials than proton reduction. The monomers are chromophore amphiphiles based on a diareno-fused ullazine core that undergo supramolecular polymerization in water to create entangled nanoscale fibers. Under 450 nm visible light these fibers sensitize a dinuclear cobalt catalyst for CO₂ photoreduction to generate carbon monoxide and methane using a sacrificial electron donor. The supramolecular photocatalytic system can generate amounts of CH₄ comparable to those obtained with a precious metal-based [Ru(phen)₃](PF₆)₂ sensitizer and, in contrast to Ru-based catalysts, retains photocatalytic activity in all aqueous media over 6 days. The present study demonstrates the potential of tailored supramolecular polymers as renewable energy and sustainability materials.

Photo-assisted electrochemical CO2 reduction using a translucent thin film electrode

Herein, we introduce a new concept of photo-assisted electrochemical CO₂ reduction through a translucent thin film electrode. The light-compatible thin film electrode directly exposes Au nanoparticle-loaded Ag nanowires to gaseous CO₂, obtaining a CO production rate of 0.7 mmol cm^-2 h^-1 with a photocurrent density of 6.05 mA cm^-2 at -1.1 V_RHE.

Process Simulations and Experimental Studies of CO2 Capture

Carbon dioxide, whose global emissions into the atmosphere have reached a maximum of about 36 billion tons per year (compared to the 6 billion tons emitted in 1950), is considered by far the main greenhouse gas (GHG) [...]

Chemisorption of CO2 by diamine-tetraamido macrocyclic motifs: a theoretical study

Although alkanolamines have been systematically utilized for CO2 capture, intensive research efforts are still required to ultimately design more efficient CO2 sorbents with appropriate sorption characteristics. In this article, we have explored a series of diamine-tetraamido macrocyclic molecules with different organic linkers, namely, pyridine, phenylene, pyrrole, furan, and thiophene, for the titled purpose using quantum chemical calculations. The optimized structures of the sequestration reaction revealed the formation of a carbamate anion within the macrocyclic cavity that was stabilized through several intramolecular interactions compared to parent amines. The reaction thermodynamics indicated that the macrocyclic compounds with pyridine, pyrrole and furan can effectively capture CO2. The results highlight the potential application of macrocyclic structures as efficient CO2 capturing agents.

Fluorinated MIL-101 for carbon capture utilisation and storage: uptake and diffusion studies under relevant industrial conditions

Carbon capture utilisation and storage (CCUS) using solid sorbents such as zeolites, activated carbon and Metal–Organic Frameworks (MOFs) could facilitate the reduction of anthropogenic CO₂ concentration. Developing efficient and stable adsorbents for CO₂ capture as well as understanding their transport diffusion limitations for CO₂ utilisation plays a crucial role in CCUS technology development. However, experimental data available on CO₂ capture and diffusion under relevant industrial conditions is very limited, particularly for MOFs. In this study we explore the use of a gravimetric Dynamic Vapour Sorption (DVS) instrument to measure low concentration CO₂ uptake and adsorption kinetics on a novel partially fluorinated MIL-101(Cr) saturated with different water vapour concentrations, at ambient pressure and temperature. Results show that up to water P/P₀ = 0.15 the total CO₂ uptake of the modified material improves and that the introduction of small amounts of water enhances the diffusion of CO₂. MIL-101(Cr)-4F(1%) proved to be a stable material under moist conditions compared to other industrial MOFs, allowing facile regeneration under relevant industrial conditions.

MIL-101(Cr)-4F(1%) proved to be a stable material under moist conditions compared to other industrial MOFs, with facile regeneration under relevant industrial conditions; plus the introduction of small amounts of water enhances the diffusion of CO₂.

Layered Double Hydroxides-Based Mixed Metal Oxides: Development of Novel Structured Sorbents for CO2 Capture Applications

Layered double hydroxide (LDHs)-based mixed metal oxides (MMOs) are widely studied as the medium to high temperature (200-400 °C) CO₂ capture sorbents. However, most of the studies are carried out using the powdered samples. To upgrade these sorbents for industrial-scale CO₂ capture, it is important to move away from the powdered form and develop structured sorbents. Moreover, the CO₂ capture properties of these sorbents need to be improved in terms of capture capacity and cycling stability. Here we are utilizing a modified amide hydrolysis method to improve the CO₂ capture capacities of LDHs-based MMOs. Subsequently, aqueous exfoliation coupled with the freeze-drying technique was utilized to develop LDHs-based novel MMOs. Exfoliated LDH nano sheets were pelletized (2 mm) to circumvent the challenges associated with powder samples when used in industrial-scale applications. The obtained pellets have an average crushing load of 11.1 N and 4.3 MPa of compressive strength, which indicate their good mechanical stability. The MMOs pellets showed a narrow distribution of pores (8-10 nm) with very good surface area (264 m²/g) and pore volume (1.27 cm³/g). They also had much improved CO₂ capture capacities at ambient pressure and both low (2.17 mmol/g, 30 °C) and medium temperature (1.43 mmol/g, 200 °C), as compared to previously reported pristine MMOs powder samples. The pelletized structured sorbents also outperformed commercial LDH-based pellets by several fold.

Acetate intercalated Mg-Al layered double hydroxides (LDHs) through modified amide hydrolysis: a new route to synthesize novel mixed metal oxides (MMOs) for CO2 capture

Layered double hydroxide (LDH) based mixed metal oxides (MMOs) are promising high temperature CO2 capture sorbents. In order to improve their CO2 capture capacity, it is crucial to bring in changes to their physicochemical properties such as morphology, particle size, surface area and activity by tuning the synthesis method. Here we report a modified amide hydrolysis method to synthesize LDHs with a mixed morphology and better CO2 capture properties. Acetate intercalated Mg-Al LDHs with two different Mg/Al ratios (3 and 4) were synthesized by employing metal hydroxides as the starting precursors and acetamide as the hydrolysing agent. The resultant LDHs crystallized in a new morphology having a combination of both fibrous and sheet like crystallites. The MMOs derived from Mg-Al-acetate LDHs retained the mixed morphology observed in the precursor LDHs. The resultant MMOs showed almost a threefold increase in the BET surface area, 316 (Mg/Al = 3) and 341 (Mg/Al = 4) m2 g-1, compared to MMOs derived from anion exchanged Mg-Al-acetate LDH (118 m2 g-1). The MMOs synthesized by acetamide hydrolysis captured 1.2 mmol g-1 and 0. 87 mmol g-1 of CO2 at 200 and 300 °C (atmospheric pressure), respectively. The CO2 capture capacity realized was increased more than twofold compared to the CO2 capture capacity of MMOs derived from anion exchanged acetate LDH (0.57 mmol g-1) tested under similar conditions. The developed MMOs showed promising CO2 capture (1.0 mmol g-1) capacity at industrially relevant CO2 concentration (14%).

Advanced High-Temperature CO2 Sorbents with Improved Long-Term Cycling Stability

Developing novel sorbents with maximum carbonation efficiency and good cycling stability for CO₂ capture is a promising route to sequester anthropogenic CO₂. In this work, we have employed a green synthesis method to synthesize CaO-based sorbents suitably stabilized by MgO and supported by in situ generated carbon under inert atmosphere. The varied amounts (10-30 wt %) of MgO were used to stabilize the CaO. The supported mixed metal oxide (MMO) sorbents were screened for high-temperature CO₂ capture under CO₂ rich (86% CO₂) and lean (14% CO₂) gas streams at 650 °C and atmospheric pressure. The MMO sorbents captured 53-63 wt % of CO₂ per gram of sorbent under 86 and 14% CO₂, accounting for about 98% carbonation efficiency, which outperforms the CO₂ capture capacity of limestone derived CaO (L-CaO) sorbents (22.8 wt %). All of the synthetic MMO sorbents showed greater capture capacity and cyclic stability when compared to benchmark L-CaO. Because of the high carbonation efficiency and cycling stability of g-Ca_0.69Mg_0.3O sorbent, it was tested for 100 carbonation/regeneration cycles of 5 min each under CO₂ lean conditions. The g-Ca_0.69Mg_0.3O sorbent showed exceptional CO₂ capture capacity and cycling stability and retained about 65% of its initial capture capacity after 100 cycles.