Efficient CO2 Research Articles

Toward Methanol Production by CO2 Hydrogenation beyond Formic Acid Formation.

ConspectusThe Paradigm shift in considering CO2 as an alternative carbon feedstock as opposed to a waste product has recently prompted intense research activities. The implementation of CO2 utilization may be achieved by designing highly efficient catalysts, exploring processes that minimize energy consumption and simplifying product purification and separation. Among possible target products derived from CO2, methanol is highly valuable because it can be used in various chemical feedstocks and as a fuel. Although it is currently produced on a plant scale by heterogeneous catalysis using a Cu/ZnO-based catalyst, a limited theoretical conversion ratio at high reaction temperatures remains an issue. In addition, a catalytic system that can be adjusted to accommodate a variable renewable energy source for the synthesis of methanol is more desirable than current continuous-operation systems, which require a reliable energy supply. Recently, significant progress has been made in the field of homogeneous catalysis, which primarily relies on an indirect route to synthesize methanol via the hydrogenation of carbonate or formate derivatives in the presence of additives and solvents. However, homogeneous catalysis is inappropriate for industrial-scale methanol production because of the inefficient separation and purification processes involved.In this Account, we demonstrate a novel approach for methanol production under mild reaction conditions by CO2 hydrogenation catalyzed by multinuclear iridium complexes under heterogeneous gas-solid phase conditions without any additives and solvents. One of the aims of this Account provides insights for overcoming the barriers for efficient CO2 hydrogenation by focusing on catalyst design, specifically by incorporating varying functionalities into the ligand. The fundamental strategy entails activating hydrogen molecule and enhancing the hydricity of the resulting metal-hydride species, which is based on the following two concepts of catalyst design: (i) Activating a metal-hydride by electronic effects; and (ii) accelerating H2 heterolysis. We have elucidated the mechanism for accelerating H2 heterolysis using a state-of-the-art catalyst that contains an actor-ligand that responds to or participates in catalysis as opposed to a classical spectator-ligand.We have also demonstrated a novel heterogeneous catalysis using a molecular catalyst as a key step for the hydrogenation of CO2 to methanol beyond formic acid formation. The dehydrogenation of formic acid as a reverse reaction of formic acid hydrogenation is strongly favored in acidic aqueous solution. To circumvent the equilibrium limitation, we have envisioned an alternative route that both prevents the liberation of formic acid into the reaction medium, and develops a multinuclear complex to facilitate the transfer of multiple reactive hydrides. The unconventional gas-solid phase catalysis is capable of preventing the liberation of formate species and promoting further hydrogenation of formic acid through multihydride transfer.This novel catalytic system, which is the fusion of a molecular catalyst in heterogeneous catalysis, provides high performance for methanol synthesis through a sophisticated catalyst design and straightforward separation processes. A detailed mechanistic analysis of molecular catalysts in the gas phase would lead to significant progress in the field of Surface Organometallic Chemistry (SOMC).

Facilitating photocatalytic CO2 methanation via synergetic feed of photon-induced carriers and reactants over S-scheme BiVO4@TiO2 nanograss/needle arrays

Herein, a unique structure BiVO4@TiO2 nanograss/needle arrays S-scheme heterojunction photocatalyst for CO2 photoreduction reaction was created. The photocatalyst can drive electrons to the reactive spots spontaneously and continuously, which effectively tackles the problem of severe recombination and disordered migration of photogenerated carriers. Theoretical calculations and experimental results demonstrate that adding BMIM-BF4 ionic liquid to generate BMIM-*CO2 intermediate promotes CO2 activation and enrichment of reactants concentration around the catalytic sites. Benefiting from the sufficient electron supply of catalytic sites and reinforced reactants supply in the interfacial microenvironment, the BiVO4@TiO2 photocatalyst shows high selectivity and activity of CO2-to-CH4 conversion. The CH4 selectivity increased to 57.3 % (132.7 μmol m-2h−1) and the methanation activity was increased by 8.6 times in the 5.0 % BMIM-BF4 aqueous solution. Significantly, the BiVO4@TiO2 NNAs catalyst obtains a solar-to-fuels energy efficiency of ∼ 0.46 ‰ under ultraviolet-enhanced light sources without any sacrificial agent or co-catalyst. This work displays the relationship between reaction process factors (electron supply, CO2 molecule, and proton supply) and CO2 photoreduction activity and selectivity, giving new insight into achieving efficient CO2 photoreduction conversion.

In-situ construction of Bi-MOF-derived S-scheme BiOBr/CdIn2S4 heterojunction with rich oxygen vacancy for selective photocatalytic CO2 reduction using water

In this study, a highly selective MOF-BiOBr/CdIn2S4 (MOF-BiOBr/CIS) heterostructure with CdIn2S4 nanosheets grown in situ on the tubular structure derived from Bi-MOF-based BiOBr was successfully constructed using a hydrothermal method. Under simulated solar light without sacrificial or photosensitizing agents, the 20-MOF-BiOBr/CIS composite exhibited excellent photocatalytic CO2 performance, achieving production rates of 30.18 μmol‧g−1‧h−1 for CO and 1.50 μmol‧g−1‧h−1 for CH4. Compared to pure MOF-BiOBr and CdIn2S4, the CO production rates were increased by approximately 9 and 116 times, respectively. It was revealed that the 20-MOF-BiOBr/CIS composite with rich oxygen vacancy exhibited close interfacial contact and efficient charge transfer. The formation of MOF-BiOBr/CdIn2S4 heterojunction thereby provided efficient CO2 photocatalytic reduction. The CO selectivity of 20-MOF-BiOBr/CIS reached 83.4 %, and the MOF-BiOBr/CIS heterojunction exhibited good stability over multiple cycles. Furthermore, a mechanism for enhanced photocatalytic CO2 reduction by the MOF-BiOBr/CIS heterojunction was also proposed.

Regulatory Network of the Late-Recruited Primary Decarboxylase C4NADP-ME in Sugarcane.

In agronomically important C4 grasses, efficient CO2 delivery to Rubisco is facilitated by NADP-malic enzyme (C4NADP-ME), which decarboxylates malate in bundle sheath cells. However, understanding the molecular regulation of the C4NADP-ME gene in sugarcane (Saccharum spp.) is hindered by its complex genetic background. Enzymatic activity assays demonstrated that decarboxylation in sugarcane Saccharum spontaneum predominantly relies on the NADP-ME pathway, similar to sorghum (Sorghum bicolor) and maize (Zea mays). Comparative genomics analysis revealed the recruitment of eight core C4 shuttle genes, including C4NADP-ME (SsC4NADP-ME2), in the C4 pathway of sugarcane. Contrasting to sorghum and maize, the expression of SsC4NADP-ME2 in sugarcane is regulated by different transcription factors (TFs). We propose a gene regulatory network for SsC4NADP-ME2, involving candidate TFs identified through gene co-expression analysis and yeast one-hybrid experiment. Among these, ABA INSENSITIVE5 (ABI5) was validated as the predominant regulator of SsC4NADP-ME2 expression, binding to a G-box within its promoter region. Interestingly, the core element ACGT within the regulatory G-box was conserved in sugarcane, sorghum, maize, and rice (Oryza sativa), suggesting an ancient regulatory code utilized in C4 photosynthesis. This study offers insights into SsC4NADP-ME2 regulation, crucial for optimizing sugarcane as a bioenergy crop.

Fabrication of a cost-effective metal oxide-based adsorbent from industrial waste slag for efficient CO2 separation under flue gas conditions

Efficient and affordable adsorbents for CO2 capture are essential in implementing carbon capture technology to mitigate the negative impact of greenhouse gas emissions. This study focuses on synthesizing new nanoporous adsorbents from industrial waste slag using a simple and cost-effective coprecipitation method. In this method, raw slag was milled for 48 h and used as a benchmark for comparing two newly synthesized adsorbents. Selectivity and pure gas isotherm experiments were conducted for all adsorbents in the 25–65°C temperature range and under harsh industrial conditions of 65°C and 15 % CO2. This study utilized the response surface methodology (RSM) to optimize the CO2 adsorption parameters. Specifically, the optimized adsorption conditions were determined for the 15/85 % CO2/N2 condition, and the optimal values for pressure and temperature were found to be 5 bar and 45°C, resulting in CO2/N2 selectivity of 5.65. The NH3-slag adsorbent was identified as the superior choice based on its selectivity and maximum adsorption capacity. The maximum adsorption capacity and cyclic efficiency were determined to be 4.15 mmol/g and 98.1 %, respectively, at a temperature, pressure, and composition of 45°C, 5 bar, and 15 % CO2. Isotherm and thermodynamic models were employed to further investigate the adsorption process. The isotherm results indicated that the adsorption of CO2 by adsorbents occurred heterogeneously in patch-wise sites. Meanwhile, the thermodynamic parameters showed that the process was exothermic and spontaneous, with ΔH° falling below 20 (kJ/mol), showing physisorption phenomena.

Regulation of Ir Dopant in Mo Oxides by Flame Spray Pyrolysis for Efficient CO2 Hydrogenation.

Mo carbide is recognized as one of the most promising catalyst for CO2 utilization via reverse water-gas shift (RWGS). However, it always suffered from low processing capacity, undesired products and deactivation. Herein, an Ir modified MoO3 synthesized by the flame spray pyrolysis (FSP) method exhibits higher reaction rate (63.0 gCO2·gcat-1·h-1) compared to the one made by traditional impregnation method (45.8 gCO2·gcat-1·h-1) over the RWGS reaction at 600°C. The distinguishing feature between the two catalysts lies in the chemical state and space distribution of Ir species. Ir species predominated in the bulk phase of MoO3 during the quenching process of the FSP method and were mainly in the metallic states, which revealed by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) characterizations. In contrast, the Ir introduced via impregnation method were mainly on the surface of MoO3 and in oxidized state. The regulation of Ir dopant in MoO3 catalyst by different methods determines the carbonization process to Mo carbides, and thus affects the catalytic performance. This work sheds light on the superiority of the FSP method in synthesizing Mo oxides with heteroatoms and further creating an efficient Mo-based catalyst for CO2 conversion.

Interfacially coupled Cu-cluster/GaN photocathode for efficient CO2 to ethylene conversion

Interfacially coupled Cu-cluster/GaN photocathode for efficient CO2 to ethylene conversion

In situ constructing 2D/2D layered BiOBr/Bi2O2CO3 heterostructure for efficient photocatalytic reduction CO2 to CO

Photocatalytic reduction of CO2 to valuable energy materials is necessary for sustainable development. It is a considerable challenge to prepare photocatalysts for CO2 photoreduction with excellent separation capability of carriers by simple way. Herein, the BiOBr/Bi2O2CO3 type-II heterostructure was constructed by in situ conversion at room temperature. Combining the advantages of the 2D/2D layered structure can form a close contact interface and the type-II heterostructure can facilitate the transport of photogenerated charges, the BiOBr/Bi2O2CO3 composite showed significant enhancement in photocatalytic CO2 reduction performance. The most obvious performance enhancement was observed for 2.0-BiOBr/Bi2O2CO3, where CO yield could reach 29.55 μmol·g−1 for 3 h under light irradiation, it is 11 and 4 times higher than Bi2O2CO3 and BiOBr, respectively. And the sample exhibits excellent cycling stability in photocatalytic tests. In situ Fourier Transform Infrared spectroscopy confirmed that the important intermediates of the reaction are *COOH and *CO. The photocatalytic reduction mechanism of CO2 to CO in the BiOBr/Bi2O2CO3 type-II heterostructure was further analyzed. This study provides feasible solutions for selecting photocatalytic materials and designing facile preparation of efficient 2D/2D catalysts for photocatalytic reduction of CO2.

A Robust Adenine-Based Microporous Metal-Organic Framework with Hydrophobic Alkyl Groups and Abundant Lewis Basic Sites for CO2/N2 Separation.

The development of a chemically robust metal-organic framework (MOF) with appropriate pore nanospace for efficient CO2 capture and separation from flue gas under humid conditions is sought after. Herein, an adenine-based microporous MOF, Cu-AD-SA, bearing abundant Lewis basic sites and alkyl groups has been utilized to capture and separate CO2 from CO2/N2 gas mixtures. The introduction of alkyl groups enable Cu-AD-SA with high chemical stability. The confined pore nanospace involving small pore size and functionalized pore surface decorated by Lewis basic amino and alkyl groups bestows the framework with stronger CO2 affinity versus N2, thus resulting in a high CO2/N2 separation performance even at high operating temperature (323 K) and humidity (80%), as evidenced by breakthrough experiments. Moreover, molecular modeling studies were implemented to establish the adsorption mechanism, in which the ditopic aliphatic carboxylic acids and adenine linkers collaboratively play a vital role in the separation of CO2/N2 gas mixtures via C-H···OCO2, CCO2···O, CCO2···N, and CCO2···π interactions.

Hierarchically porous MgO/biochar composites for efficient CO2 capture: Structure, performance and mechanism

For enhancing the CO2 uptake performance of MgO-based materials, hierarchically porous MgO/biochar composites were prepared using a microwave-assisted hydrothermal method. The CO2 adsorption properties was investigated in detail and the adsorption mechanism was revealed by considering structure − function relationships and performing density functional theory calculations. The MgO/biochar-1 had hierarchical pore structure and high specific surface area (1453 m2·g−1) with abundant narrow micropores (<1.0 nm), facilitating the adsorption of CO2. The results demonstrated that MgO/biochar-1 exhibited the highest CO2 capture capacity of 6.65 mol⋅kg−1 (273 K, 1 bar) and excellent selectivity for CO2/N2 (96.70 at CO2/N2 = 15:85, v/v). After 3 cycles, the adsorption capacity of MgO/biochar-1 still remained at 5.70 mol⋅kg−1 (273 K, 1 bar), suggesting the well cycling performance. The results of density functional theory calculation indicated that the oxygen-containing functional groups and MgO particles substantially enhanced the CO2 capture performance due to the enhanced interactions between MgO/biochar and CO2. This study provides novel insights for the construction of efficient and cheap solid adsorbents for CO2 capture.

Ti[sbnd]F bridged IL-CuCQDs-F/TiO2 inverse opal composite for boosting CO2 visible-photo reduction via slow photon effect

Photocatalytic reduction of CO2 exhibits unsatisfactory photocatalytic performance owing to the inefficient separation of photogenerated electron-hole pairs, low CO2 capture efficiency and limited visible light absorption on most photo-catalysts. Herein, TiF bridged IL-CuCQDs-F/TiO2 inverse opal composite (IO-CFTi) was constructed for boosting CO2 visible-photo reduction via slow photo effect. In this work, ethylenediaminetetraacetic acid (EDTA(Cu)) and imidazole ionic liquid 1-(2-Hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([HOEtMIM][BF4]) were employed to confine grow of IL-CuCQDs-F within TiO2 inverse opal supporter via TiF bonds connection. Unique IL-CuCQDs-F efficiently expended light absorption towards visible region, and the confined growth of IL-CuCQDs-F within the TiO2 inverse opal cavity achieved the photoelectric conversion and efficient CO2 capture. Moreover, their TiF bonding interface of IO-CFTi assisted photogenerated electron transportation from TiO2 to CO2 for its reduction in this system. Consequently, IO-CFTi achieved a substantially increased CO production rate of 78.1 μmol·h−1·g−1 with 98 % selectivity. This improved performance in CO2 photoreduction positions the nanocomposite as a promising material for preservation of the environment and conversion of energy.

Reversible Multi-Complexation of CO2 to Alkaline Earth Metal Ion-Pair at 400 ppm and 298 K.

The efficient capture of low-pressure CO2 remains a significant challenge due to the lack of established multi-complexation of CO2 to active sites in microporous materials. In this study, we introduce a novel concept of reversible multi-complexation of CO2 to alkaline earth metal (AEM) ion pairs, utilizing a host site in ferrierite-type zeolite (FER). This unique site constrains two AEM ions in proximity, thereby enhancing and isotopically spreading their electrostatic potentials within the zeolite cavity. This electrostatic potential-engineered micropore can trap up to four CO2 molecules, forming M2+-(CO2)n-M2+ (n = 0-4, M = Ca, Sr, Ba) complexes, where each CO2 molecule is stabilized by interactions between terminal oxygen (Ot) in CO2 and the AEM ions. Notably, the Ba2+ pair site exhibits higher thermodynamic stability for multiple adsorptions due to the optimal binding mode of Ba2+-Ot-Ba2+. Through high-accuracy energy calculations, we established the relationship among structure, CO2 uptake, and operating temperature/pressure, demonstrating that the Ba2+ pair site can reversibly capture four CO2 molecules even at concentrations as low as 400 ppm and at 298 K. The findings in the present study provide a new direction for developing efficient CO2 adsorbents.

Chemically bonded to construct S-scheme CNQDs/Bi2WO6 heterostructure: The Bi-N bonds as interfacial electronic channel boosting the efficient photocatalytic CO2 reduction under simulated sunlight

Photoinduced carrier separation efficiency plays a crucial role in determining the photocatalytic activity of photocatalysts, but it remains a challenge to accurately and efficiently control charge separation. Hence, we successfully prepared S-scheme CNQDs/Bi2WO6 heterostructure via a simple hydrothermal method. The theoretical calculations demonstrate that Bi-N bonds at the interface between CNQDs and Bi2WO6 serve as an electron transfer channel to facilitate charge transfer at the atomic level, which plays a vital role in driving the photoreduction of CO2 to CO. Interestingly, S-scheme heterostructure not only remains strong reducing ability of CNQDs, but also significantly reduces the energy barrier of *CO2 *COOH and release the product CO easily. The CO yield of the CNQDs/Bi2WO6 sample (26.24 µmol/g) was 11 times higher than that of the pure Bi2WO6 (2.43 µmol/g) without any sacrificial agents under 300 W xenon lamp. This work highlights the critical role of chemical bonding interfaces in the design of efficient S-scheme heterostructure photocatalysts.

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

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

The Reconstruction of Bi2Te4O11 Nanorods for Efficient and pH-universal Electrochemical CO2 Reduction.

The electrochemical CO2 reduction reaction (CO2RR) to generate chemical fuels such as formate presents a promising route to a carbon-neutral future. However, its practical application is hindered by the competing CO production and hydrogen evolution reaction (HER), as well as the lack of pH-universal catalysts. Here, Te-modified Bi nanorods (Te-Bi NRs) were synthesized through in situ reconstruction of Bi2Te4O11 NRs under the CO2RR condition. Our study illustrates that the complex reconstruction process of Bi2Te4O11 NRs during CO2RR could be decoupled into three distinct steps, i.e., the destruction of Bi2Te4O11, the formation of Te/Bi phases, and the dissolution of Te. The thus-obtained Te-Bi NRs exhibit remarkably high performance in CO2RR towards formate production, showing high activity, selectivity, and stability across all pH conditions (acidic, neutral, and alkaline). In a flow cell reactor under neutral, alkaline, or acidic conditions, the catalysts achieved HCOOH Faradaic efficiencies of up to 94.3 %, 96.4 %, and 91.0 %, respectively, at a high current density of 300 mA cm-2. Density functional theory calculations, along with operando spectral measurements, reveal that Te manipulates the Bi sites to an electron-deficient state, enhancing the adsorption strength of the *OCHO intermediate, and significantly suppressing the competing HER and CO production. This study highlights the substantial influence of catalyst reconstruction under operational conditions and offers insights into designing highly active and stable electrocatalysts towards CO2RR.

Encapsulating Halide Perovskite Quantum Dots in Metal–Organic Frameworks for Efficient Photocatalytic CO2 Reduction

Halide perovskite has shown great potential in photocatalysis owing to its diversity, suitable energy band alignment, rapid charge transfer, and excellent optical properties. However, poor stability, especially under humid conditions, hinders their practical application in photocatalysis. In this work, we report the encapsulation of inorganic–organic hybrid perovskite QDs into MIL-101(Cr) through an in situ growth strategy to prepare a series of MAPbBr3@MIL-101(Cr) (MA = CH3NH3+) composites. The perovskite precursors, i.e., MABr and PbBr2, were successively introduced into the pores of MOF, where the perovskite quantum dots were self-assembled in the confined environment. In photocatalytic CO2 reduction, 11%MAPbBr3@MIL-101(Cr) composite displayed the best performance among the composites with a total CO and CH4 yield of 875 μmol g−1 in 9 h, which was 8 times higher than that of the pure MAPbBr3. Such high gas production efficiency could be maintained for 78 h at least without structural and morphologic decomposition. The remarkable stability and catalytic activity of composites are mainly due to the synergistic effect and improved electron transfer between MAPbBr3 and MIL-101(Cr). Moreover, these composites revealed a novel mechanism, showing switched CH4 selectivity with the controlling of the perovskite location and contents. Those with perovskites encapsulated in the mesopores of MIL-101(Cr) were more preferential for CO production, while those with perovskites encapsulated in both meso- and micropores could produce CH4 dominantly.

Near-infrared-responsive sea-urchin-like Ag6Si2O7/Bi19Br3S27 S-scheme heterojunction for efficient CO2 photoreduction

The construction of S-scheme heterojunctions effectively facilitates the spatial separation of photogenerated charge carriers for their involvement in photoreactions. However, the inefficient utilization of solar energy in these heterostructures is often due to unfavorable band-edge positions and suboptimal charge transport dynamics, which result in low photocatalytic efficiency when considering kinetic factors. In this study, sea urchin–like Bi19Br3S27/Ag6Si2O7 S-scheme heterojunctions are fabricated, which exhibit excellent CO2 photoreduction performance under ultraviolet, visible, and near-infrared (NIR) light illumination. Experimental data and density functional theory calculations confirm the S-scheme charge transfer mechanisms, which enable the efficient separation of photogenerated carriers for CO2 reduction. Consequently, the optimized Ag6Si2O7/Bi19Br3S27 heterostructures exhibit superior CO2 photoreduction activity under NIR light irradiation. This approach offers a strategy for designing advanced NIR-light-responsive photocatalysts for efficient CO2 photoreduction.

Entropy‐Driven Carbon Dioxide Capture: The Role of High Salinity and Hydrophobic Monoethanolamine

Addressing atmospheric CO2 levels during the transition to carbon neutrality requires efficient CO2 capture methods. Aqueous amine scrubbing dominates large‐scale flue gas capture but is hampered by the energy‐intensive regeneration step, sorbent loss, and consequent environmental concerns with volatile amines. Herein, hydrophobic non‐volatile alkylated monoethanolamine (MEA) is introduced as a water‐lean CO2 absorbent in brine. The effects of alkylation of MEA, salinity, and aggregation of absorbents on the improved CO2 capture process are systematically investigated. The CO2 absorption facilitates spontaneous self‐aggregation of hydrophobic absorbents, which increases the entropy of water in high‐ion strength solutions. This effect is controlled by the salinity of aqueous solutions, affording comparative gravimetric CO2 uptake performance to benchmark MEA. It is experimentally verified that the hydrophobicity of alkylated MEAs in saline water is responsible for facile absorption, and also for mild regeneration conditions. Therefore, the entropy‐driven approach minimizes absorbent evaporation, corrosion, and decomposition, thus paving the way to realize energy‐efficient carbon capture.

Numerical simulation of gasifier optimization for combined hydrogen production and carbon reduction in a chemical looping gasification (CLG) system

Chemical looping gasification (CLG) for combined hydrogen production and carbon capture represents a significant pathway for the clean, low-carbon utilization of traditional fossil fuels. Currently, a significant knowledge gap remains concerning the interplay between reactor configuration optimization and the complex gas–solid interactions in the CLG systems. This study integrates reactive computational fluid dynamics-discrete element method (CFD-DEM) simulations with a coarse-grained model (CGM) to analyze 3D coal-based CLG systems. The spatiotemporal distributions of gas–solid flow dynamics and thermochemical characteristics are revealed. It is found that increasing the gasifier height enhances fuel conversion and hydrogen production but compromises CO2 absorption. Smaller reactor diameters induce excessively rapid gas–solid flows, leading to incomplete fuel conversion and reduced hydrogen yield, while larger diameters cause uneven flows, significantly deteriorating hydrogen production and carbon absorption efficiency. Based on the simulation findings, the optimal height-to-diameter ratio for the gasifier in a CLG system is approximately 28.8, optimizing H2 production while maintaining efficient CO2 absorption. Moreover, the superficial gas velocity has a multifaceted influence on the hydrogen production and carbon reduction performance in the CLG process, necessitating a comprehensive consideration of its effects on fuel reaction time, gas–solid interactions, and other factors.

Deciphering the transfer mechanisms for CO2 absorption into binary blended solutions

A thorough understanding of the mechanisms involved in CO2 chemical absorption is crucial for the development of efficient CO2 capture technologies. Due to the insufficient insight into the interaction mechanism of different components in blended solutions, CO2 absorption reactions were often categorized as unidirectional transfer between absorption products. In this study, the CO2 absorption performance of binary blended solutions, including piperazine (PZ)/n-methyldiethanolamine (MDEA), ethanolamine (MEA)/MDEA, ammonia (NH3)/MDEA, PZ/potassium carbonate (K2CO3), and NH3/K2CO3, was investigated using a combination of experimental and computational methods. The CO2 absorption mechanisms of “competitive reaction”, “transfer reaction” and “parallel reaction” in the binary blended solution system were proposed. Kinetic experiments revealed that different blended solutions had varying impacts on the process of CO2 absorption. Among them, PZ/MDEA and MEA/MDEA solutions reduced the absorption rates by an average of 8% and 25%, respectively, compared to PZ or MEA component solutions. NH3/MDEA and PZ/K2CO3 solutions had absorption rates similar to those of single NH3/PZ component solutions. NH3/K2CO3 solutions, on the other hand, exhibited an average increase of 17% in absorption rates compared to NH3 solutions. Quantum mechanical (QM) methods were employed to evaluate of the absorption products and key processes in terms of kinetics and thermodynamics. Quantitative 13C NMR analyses were conducted to further investigate the interactions between components and the pathways of mass transport in blended solutions, which demonstrated proton transfer and CO2/-COO transfer between adsorption products. This study highlights an accurate description of the transfer mechanisms of various blended systems for the enhanced CO2 capture.