Perovskite CaMnO3 is a promising thermochemical energy storage candidate. In this work, to optimize the redox performance of CaMnO3, Sr and Fe were co-doped at the A/B sites of CaMnO3 to balance the stability and thermochemical energy storage density. (Sr0.05Ca0.95)(Fe0.05Mn0.95)O3-δ (SCFM5) and (Sr0.10Ca0.90)(Fe0.10Mn0.90)O3-δ (SCFM10) were synthesized via a modified citrate auto-combustion method. Scanning Electron Microscope (SEM) revealed a loose and porous structure in the composites, which contributes to an increased specific surface area and mitigates the particle agglomeration. Thermogravimetric analysis (TGA) results indicate the reversible mass loss of both SCFM5 and SCFM10 at varied oxygen partial pressures. At pO2 = 10-3 atm and T = 1100°C, SCFM5 and SCFM10 exhibit the highest thermochemical energy storage densities of 535 ± 55 kJ/kg and 499 ± 49 kJ/kg, respectively. And for SCFM10, there is no obvious degradation in thermochemical energy storage density and structural integrity over redox cycles. Kinetic analysis reveals that the linear relationship between ln[-ln(1-X)] and lnt for SCFM5 and SCFM10, fitted by the Hancock and Sharp method, exhibits two reaction zones at different temperatures, corresponding to the Avrami-Erofeyev (A2) for Nucleation and Growth Model and the 3-D diffusion (D3) for Diffusion-Limited Model, respectively. SCFM10 exhibits a lower activation energy (Ea = 18.2 ± 0.21 kJ/mol) and pre-exponential factor (A ≈ 4.3 × 10-3 s−1) in the second reaction zone compared to SCFM5, thus enhancing the redox reaction rate. This work provides a promising approach for the modification of CaMnO3-based materials to achieve higher thermochemical energy storage density.

Direct air capture (DAC) of CO2 requires sorbents that combine high uptake, fast kinetics, and low-energy regeneration. Here, we report a selective confinement strategy to fabricate a KOH-functionalized activated carbon cloth (KOH-O-ACC) that achieves these goals, delivering both fast adsorption kinetics and low-temperature regenerability. By selectively removing surface-deposited species while preserving KOH confined within the micropores, this approach shifts the active species from undesirable surface accumulation into the micropores. The resulting sorbent delivers a CO2 uptake of 0.358 mmol/g under realistic DAC conditions (400 ppm CO2, 30 degrees C) and can be regenerated at low temperatures of 80-100 degrees C. Over 50 adsorption-desorption cycles, the material retains approximately 89% of its initial capacity and exhibits superior oxidative stability compared to amine-based sorbents. Preliminary mechanistic insights suggest that the strong chemisorption under dry conditions may be related to confined water retained within the material. This work demonstrates that precise spatial control of active species is a critical design principle for developing energy-efficient and durable DAC sorbents.

The core of the CO2 capture technology based on chemical absorption lies in the optimization of the performance of the absorbent. However, the current methods and indicators used to evaluate the performance of absorbents are limited, particularly those that incorporate energy consumption. This paper proposes a multi-criteria rapid preliminary screening method for absorbents, covering seven key indicators of the amine absorbent for CO2 capture, to characterize CO2 reaction performance, energy consumption performance, physical properties, and economic performance. The Analytic Hierarchy Process (AHP)-entropy weight Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method was used to rapidly screen 18 amine absorbents in three categories. The results showed that the evaluation method was primarily suitable for aqueous amines and could also be extended to other types of absorbents. In addition, the combined subjective and objective weighting results indicated that the quasi-cycle capacity, absorption heat, and boiling point indicators were highly important for amine absorbents. The comprehensive index (CI) demonstrated that among the three amine categories, AEEA, PS, and TEDA-DMEN were the best absorbents for CO2 capture, respectively. In particular, TEDA-DMEN exhibited a large quasi-cycle capacity (0.560 mol/mol), as well as low CO2 absorption heat (66.87 kJ/mol), sensible heat (37.61 kJ/mol), and cost (0.104 $/g). This paper provides a theoretical basis and methodological support for developing high-efficiency, low-energy, and low-cost absorbents for CO2 capture.

Calcium looping (CaL) is a promising technology for thermochemical energy storage (TCES), benefiting from the high energy storage density and operating temperature of CaO-based heat carriers. However, CaO suffers from severe sintering and low optical absorptance. In this work, Mg/Al/Mn mono-, binary-, and ternary-doped CaO-based microspheres were synthesized via dual-fluid spray pyrolysis (SP) and spray combustion (SC), respectively. The effects of doping schemes on cyclic energy storage, optical absorption, and microstructure were systematically investigated. Mg mono doping refined grains and optimized the pore structure, with 30 wt % MgO as the optimum. Al mono doping formed Ca3Al2O6, reducing reactivity but improving cyclic stability. Mg-Al binary doping displayed a synergistic effect, balancing energy storage density and stability. With a total doping content of 20 wt %, introducing Mn boosted energy storage performance and optical absorption: The Mg-Mn system exhibited superior reactivity with Ca2MnO4 formed, and the SP-derived sample with 15 wt % MgO/5 wt % MnO2 showed a 50-cycle accumulated energy storage density of 104 kJ/g. The Al-Mn system produced CaMnO3 with enhanced stability, and the maximum optical absorptance reached 87.41%. Mg-Al-Mn ternary doping yielded microspheres with balanced overall performance. The SC-derived sample with 5 wt % MgO/5 wt % Al2O3/10 wt % MnO2 showed a 50-cycle decay rate of 9.94% and average solar absorptance of 79.19%. All microsphere surfaces possessed uniform elemental distribution. Parametric comparison revealed that SP favored porous structures for higher energy storage density, whereas SC improved crystallinity, cyclic stability, and optical absorption, though requiring more anti-sintering dopants to offset the effects of high-temperature synthesis.

Calcium-based adsorbents hold great promise for large-scale CO2 capture. However, CaO pellets suffer fragmentation when stored in moist air, limiting their application. Numerous studies demonstrate that the presence of water significantly affects the structural integrity of adsorbent pellets. However, most of these studies focus on high-temperature conditions, while limited attention to moist air conditions. This study investigated the effect of different hydration pathways on the structural integrity of CaO pellets and revealed the fragmentation mechanism under moist air. Multiscale characterizations showed that CaO pellets exposed to moist air or liquid water underwent severe fragmentation, primarily caused by liquid-water hydration reactions. FT-IR and TGA results confirmed the presence of residual water in the fragmented pellets, while Rietveld refinement showed a significant drop in crystallinity and rise in microstrain. These changes compromised the structural integrity of pellets. In contrast, the pellets undergoing high-temperature steam hydration retained structural integrity, showing high crystallinity and low microstrain. Based on this, a hydrothermal shell-core strategy was proposed to enhance the anti-fragmentation performance of CaO pellets. A dense Ca(OH)2 shell formed via high-temperature steam hydration isolated the CaO core from moist air, significantly enhancing structural integrity. Pellets with over 60 % hydration conversion retained 74.07 % structural integrity after 48 h of exposure to moist air (30 degrees C and 85 % RH), three times higher than unhydrated pellets, while CO2 capture capacity of the revised pellets surpassed 0.6 g CO2/g adsorbent. These findings provide both mechanistic basis and design strategy for the production, transportation, and storage of calcium-based adsorbent pellets in moist environments.

In gas purification processes, absorption in packed columns is one of the most commonly used and highly efficient methods for gas removal. However, the prediction of mass transfer performance in packed columns often suffers from significant uncertainties, which has long been a critical challenge in industrial design, process analysis, and simulation. To address this issue, the present study introduces the concept of ineffective porosity (su) and systematically evaluates its role in improving the prediction accuracy of mass transfer performance in packed columns. First, the value of su was determined using the Billet inverse calculation method, and the results demonstrated an approximately linear relationship between su and the liquid holdup (H). Subsequently, experiments were conducted to examine the effects of operating parameters on the effective interfacial area (av) and mass transfer performance. Incorporating su into the av model reduced the absolute average deviation (AAD) from 13.9% to 9.6%. Similarly, the incorporation of su into various mass transfer models has been shown to enhance their predictive accuracy. Finally, the mass transfer mechanism of CO2 absorption by amine solutions was explored, demonstrating that the process is controlled by reaction kinetics. These findings not only highlight the critical role of ineffective porosity in mass transfer modeling but also provide methodological guidance for the precise design, process optimization, and industrial application of packed columns.

This work was a follow-up to "A Novel Mold-Based Granulation of Calcium-Based Heat Carriers with High Uniformity and Wear Resistance: Method Proposal and Process Optimization". Aiming to address the issue of cyclic degradation in the heat storage performance of the prepared pellets, the extrusion-rounding granulation method was adopted to carry out dry modification research. Multiple characterization approaches and targeted performance test methods were adopted to conduct a systematic comparison of the composite calcium-based pellets, with a focus on their pore structure, heat storage and release performance, mechanical strength, and thermal conductivity. The results indicated that doping of inert materials could alleviate the damage to the pore structure of heat carriers caused by external forces during the extrusion process, thereby retaining a more abundant pore structure; among them, the specific surface area of Al-CaO was 2.25 times that of CaO. In terms of heat storage performance, the Zr-CaO sample exhibited better sintering resistance owing to the formation of CaZrO3 which had a high Tammann temperature, and the degradation rate of its heat storage density (HSD) after 20 cycles was 67.75%. In terms of heat storage performance, the Zr-CaO sample exhibits better sintering resistance owing to the formation of CaZrO3 with a high Tammann temperature, and the degradation rate of its HSD after 20 cycles was 67.75%. In terms of thermal conductivity, Mg-CaO showed favorable performance in both average thermal conductivity and average thermal diffusivity. Finally, the results of long-term cycling tests confirmed that the specific surface area and pore volume highlighted in previous work were key performance-influencing parameters; a larger specific surface area and pore volume could increase the HSD of the heat carrier after ultimate decay.

Calcium looping is a promising technology for high-temperature CO2 capture, but the rapid deactivation of CaO during repeated carbonation-calcination cycles limits its application. This study systematically investigates the deactivation behavior of CaO subjected to extended calcination at 950 degrees C, emphasizing its nonlinear and stage-dependent characteristics. The cumulative CO2 capture capacity decreases from approximately 2.7 to 1.2 g CO2 g(-1) after 48 h of calcination (approximate to 55-60% reduction), accompanied by an similar to 80% loss in BET surface area (9.97 to 1.81 m(2)/g). The deactivation proceeds through three distinct stages, with a clear boundary between 12 and 24 h, beyond which performance deterioration becomes structurally constrained. By correlating CO2 uptake with grain growth, pore evolution, and morphological reconstruction, we show that the dominant microstructural control shifts with prolonged thermal exposure. These findings provide mechanistic insight into nonlinear deactivation under prolonged high-temperature calcination.

The mechanistic understanding of peroxymonosulfate (PMS) activation by heterogeneous cobalt catalysts is shifting from radical to nonradical pathways, with High-valent cobalt-oxo species (Co(IV)=O) circumventing the oxo wall and thus attracting considerable attention. This review systematically examines electron-transfer pathway selection from Co(II) activation to Co(IV)=O through Co(III) intermediate formation from a coordination chemistry perspective and consolidates strategies spanning local coordination modulation and nonlocal interfacial coupling to overcome the oxo wall. Co(III) is reconceptualized from a passive cycle terminus into a multifunctional node capable of acting as an absentee, an obligatory bridge, a parallel competitor, or a synthetically accessible starting point. To address the challenge of unambiguous Co(IV)=O identification, we (i) evaluate the assignability limits of the phenyl methyl sulfoxide probe, 18O labeling, in situ spectroscopy, and electron paramagnetic resonance; (ii) emphasize cross-validation; and (iii) discuss dynamic pathway regulation through reaction condition tuning. The obtained insights are integrated to propose a unified coordination heterogeneity–mechanistic bifurcation framework. In this framework, each of the diverse surface coordination configurations constituting a statistical ensemble activates PMS via a pathway determined by its spin state and effective d-electron density. Further, the macroscopic distribution of reactive species is the statistical average of these coordination microenvironments. We further identify bottlenecks in synthesis homogeneity, characterization, and full-life-cycle assessment, and highlight the need to overcome challenges in quantitative structure–activity relationships, precise active-site engineering, and real-time reaction monitoring. The proposed framework offers a conceptual roadmap for rationally designing catalysts circumventing the oxo wall.

The rapid sintering and performance degradation of calcium-based adsorbents during cyclic CO2 capture represent a major bottleneck limiting their large-scale application. While ball milling combined with inert oxide doping is an effective anti-sintering strategy, most studies focus on single-oxide doping systems using high-purity materials. In industrial applications, cost-effective Al2O3 and SiO2-rich minerals or composite supports are commonly used as dopant sources. However, the synergistic mechanism between ball milling and such multi-component co-doping remains poorly understood, hindering the rational design of high-performance adsorbents. To address this, we investigate the synergistic modification mechanism of ball milling with Al2O3 and SiO2 co-doping. The results indicated that the synergistically modified sample (80Ca-10Al/10Si) exhibited excellent sintering-resistant stability, retaining a CO2 capture capacity remaining at 0.36 g CO2/g adsorbent after 50 cycles. And ball milling achieved nanoscale homogeneous dispersion of Al and Si components within the CaO matrix. This subsequently facilitated the in-situ formation of an interwoven composite inert skeleton consisting of Ca3Al2O6 and CaSiO3 during cycling. This structure effectively pinned the CaO grain boundaries, suppressing high-temperature sintering. Concurrently, the modification increased the surface oxygen vacancy concentration, specific surface area and pore volume of the adsorbent. This change reduced the activation energy of the fast reaction stage by more than 40%, and consequently, a marked improvement in reaction kinetics. This work elucidates the synergistic mechanism of ball milling and multi-component doping in constructing a sintering-resistant nanocomposite structure, providing a new approach for designing calcium-based CO2 adsorbents with high stability and reactivity.

Sterically hindered amines (SHAs) offering high theoretical capacity and reduced regeneration energy, yet their molecular mechanism, especially in non-aqueous solvents, remains unclear. This study bridges this gap by combining computational and experimental approaches. This involved a systematic investigation of diverse amine classes. We introduced a set of molecular descriptors to quantify the steric hindrance effect, correlated them with key structural features, and rigorously linked these descriptors to the absorption performance through Quantitative Structure-Activity Relationship (QSAR) analyses, encompassing capacity, rate, and reaction thermodynamics. A systematic investigation reveals that the molecular features, including of substituent type and number, hydrogen bonding, and ring structures, affect steric hindrance. More importantly, a dual effect of steric hindrance was proposed: Steric hindrance alters the conventional zwitterionic mechanism, shifting the reaction toward an alcoholysis pathway. This substitution enhances the thermodynamic process by promoting the conversion of carbamate into alkyl carbonate, thereby raising the theoretical CO2 loading to 1 mol/mol. At the same time, it suppresses the kinetic process by reducing the collision efficiency of CO2. These fundamental understanding provide design principles for novel absorbents based on SHAs with high CO2 capacity and low regeneration energy requirements, paving the way for more efficient carbon capture technologies.

Potassium-based solid adsorbents have shown considerable potential for post-combustion CO2 capture. However, their performance is often constrained by the agglomeration of the active component during preparation and adsorption processes. To address this challenge, this study proposes a strategy employing KHCO3 as the precursor dispersed on the non-porous SiO2 support to mitigate active component agglomeration and enhance CO2 capture performance. The resulting adsorbents were systematically characterized and evaluated under simulated post-combustion conditions. Results reveal that SiO2 acts as an effective dispersive support, enabling exceptionally high active phase loadings up to 70wt%, far exceeding the optimal loadings typically reported in the literature. The KHCO3-derived adsorbents exhibit superior performance, achieving near-complete active component utilization and a maximum CO2 capacity of 4.21mmol/g at 60wt% loading, significantly outperforming K2CO3-derived counterparts. Structural analyses confirm that this enhanced performance originates from the porous structure formed during the thermal decomposition of KHCO3. Furthermore, no crystalline K-Si byproducts or hydrated phases were detected during the CO2 adsorption process, contributing to outstanding cyclic stability with maintained structural integrity after 20 cycles. This work highlights the importance of coordinated support and precursor selection for advancing potassium-based CO2 capture materials.

As a high-energy-density heat storage technology, calcium-looping heat storage is limited in its application and promotion due to the poor mechanical properties of calcium-based heat carrier materials, which are prone to wear, breakage, and even elutriation in reactors. This work proposed a new granulation method for calciumbased heat carriers, where mold kneading was used to replace the spheronization step in the extrusionspheronization method. This not only improved pellets uniformity and sphericity but also ensured good mechanical strength and heat storage performance of the pellets. Simultaneous thermal analysis (STA), fieldemission scanning electron microscopy (SEM), X-ray diffraction (XRD), particle strength testing, and N2 isothermal adsorption-desorption were used to test the pellets prepared by this method in terms of pore structure, heat storage and release performance, mechanical strength, and other aspects. The results indicated that the pellets prepared by the extrusion-rounding method exhibited excellent mechanical properties, benefiting from their smooth surface and high sphericity derived from integral forming. Specifically, the rotational wear rate after 2000 cycles was only 1.32%; moreover, under severe calcination conditions, their heat storage density remained above 0.67 kJ/g even after 20 cycles. During the further optimization of the dry mixing process in the granulation method, it was found that changes in the ball-to-powder ratio affected cold welding issues during the ball milling process and exerted a significant impact on the performance of heat carriers. These findings indicated that the extrusion-rounding method was an efficient granulation technology, and the prepared heat carriers exhibited excellent heat storage and release performance, showing great application potential.

The energy-intensive regeneration process of amine solutions is the main obstacle for the CO2 capture process. Direct measurement of energy consumption during the rich amine solution regeneration process is often constrained by high labor demands and operational costs, limiting its scalability in industrial applications. To address these challenges, this study proposes an innovative framework for predicting the desorption energy consumption (Qreg) based on mass transfer kinetics and gas-liquid equilibrium theory, offering a viable alternative for optimizing energy usage in CO2 capture systems. Emphasizing practical relevance, the research systematically evaluates Qreg under varying operational conditions and decomposes it into absorption heat (Qabs), sensible heat (Qsen), and latent heat (Qlat) components within a stripper. Experimental analysis reveals that, in addition to the intrinsic thermodynamic properties of the absorbents, key operational parameters, including liquid flow rate (L), lean and rich CO2 loadings (alpha leanand alpha rich), and absorbent concentration (C), have a substantial impact on gas-liquid equilibrium and mass transfer, and thus on Qreg. By strategically optimizing these parameters within a sustainable operating window, significant reductions in Qreg can be achieved. A novel predictive framework based on gas-liquid equilibrium and mass transfer kinetics was developed to accurately predict Qsenand Qlat, achieving average absolute deviations (AAD) of 11.9% and 9.5%, respectively. This approach not only enhances predictive capability but also contributes to the development of energy-efficient CO2 capture technologies.

Calcium-based sorbents are plagued by sintering during calcium looping (CaL) cycles, which severely degrades their CO2 capture performance. To address this issue, this study proposed a novel co-supporting method for preparing calcium-based sorbent pellets. The modified sorbents were fabricated by blending Ca(OH)2, coal fly ash, and cement, followed by extruding the slurry into pellets. The performance of sorbent pellets was systematically evaluated. The results demonstrated that both coal fly ash and cement exerted a positive effect on enhancing the CO2 capture performance. Specifically, the formulation containing 10 wt% coal fly ash and 15 wt % cement exhibited the optimal comprehensive performance among all the samples: it achieved a cumulative CO2 capture capacity of 6.03 g CO2/g sorbent over 20 cycles. Additionally, this formulation retained 64.7 % of its initial CO2 capture capacity after 20 cycles, which was significantly higher than the 47.2 % retention rate of the pure CaO sorbents (100Ca). Furthermore, this modified formulation exhibited a compressive force of 69.12 N. This study revealed that coal fly ash effectively enhanced the initial carbonation conversion, while cement improved the sorbents' cyclic stability and mechanical strength. Moreover, characterization results elucidated the distinct roles of the two additives: coal fly ash functioned as an inert support, preserving the sorbents' pore structure and mitigating particle agglomeration; cement reacted with CaO to form Ca12Al14O33-an inert skeleton that supported the pore structure, thus effectively suppressing sintering.

Red mud, an industrial byproduct rich in α-Fe2O3, was employed as a support for ZIF-67-derived Co3O4 to construct composite catalysts for toluene oxidation via in-situ preparation, impregnation, and mechanical mixing. The catalyst prepared by the in-situ method, MRM-@, exhibited the highest activity, achieving a T90 of 268 °C and an apparent activation energy of 107.00kJ/mol, despite possessing the smallest specific surface area. Comprehensive characterizations revealed that the superior performance originates from the strong Co3O4/α-Fe2O3 interfacial interaction uniquely formed through the in-situ preparation. The intimate Co3O4/α-Fe2O3 contact facilitates strong interfacial interaction, which possibly involves the formation of Co-O-Fe bridge coordination structures and induces electron density redistribution within the bridging oxygen bonds toward Co, thereby increasing the Co3+/Co2+ ratio and enhancing lattice oxygen reactivity, consequently accelerating the Mars-van Krevelen redox cycle. In contrast, impregnation and mechanical mixing failed to generate sufficient sufficient interfacial interactions. These results demonstrate that the Co-O-Fe interfacial structure is the dominant factor governing catalytic performance, highlighting the potential of red mud as a low-cost catalyst support for VOC abatement.

The biphasic absorbent is considered one of the best substitutes for amine solutions because of its great potential to save energy consumption. However, high viscosity and poor CO2 capture capacity of biphasic solvents have emerged as major obstacles to their commercial use. In this work, a strategy to lower the viscosity of the CO2-rich phase was proposed. Based on this strategy, a promising biphasic solvent 2-Dimethylaminoethanol (DMEA)/2Methylaminoethanol (MAE)/H2O was developed by Triethylene glycol monobutyl ether (TGME) regulation. The results show that the maximum viscosity of the CO2-rich phase after CO2 absorption was only 8.34cp. When ignoring the phase separation enthalpy, the CO2 capture efficiency can reach 89.3 % when the energy consumption is 1.99GJ/ tCO2. Besides, the speciation concentration of DMEA/MAE/TGME/H2O with different CO2 loadings was determined by gas-liquid equilibrium theory. Based on the speciation concentration distribution, the possible reaction between CO2 and 2 mol DMEA/ 1.25 mol MAE goes through three stages. 13C NMR analysis was used to investigate the reaction mechanism and phase change behavior, and the salting-out effect was proved to be the reason for the phase change behavior of the DMEA/MAE/TGME/H2O systems. This work also shows that DMEA/MAE/TGME/H2O has a high CO2 absorption capacity and superior CO2 removal efficiency.