Lithium orthosilicate (Li4SiO4) is a promising candidate for CO2 capture. Steam is inevitably present in industrial flue gas, yet its physicochemical role in Li4SiO4-based sorbents remains insufficiently understood, particularly during regeneration. Moreover, unlike well-studied powdered sorbents, the behavior of pelletized Li4SiO4 under steam-containing atmospheres has received limited attention. This study investigates steam-assisted desorption under both CO2/H2O and N2/H2O atmospheres and systematically evaluates the influence of steam on the physicochemical evolution and cyclic stability of Li4SiO4-based sorbent pellets. A steam-rich regeneration strategy is evaluated at varying steam fractions and compared with conventional N2 purging and pure CO2 regeneration. Four operational configurations were designed to decouple the stage-specific effects of steam. The characterization results indicate that steam causes slight structural coarsening while also promoting sorption and desorption under the tested conditions. During sorption, steam was associated with surface hydroxylation and faster diffusion-controlled behavior, consistent with enhanced Li+ mobility. Steam addition during desorption also facilitated CO2 release. When steam was introduced into a CO2-containing atmosphere, decarbonation occurred at lower regeneration temperatures than under pure CO2. Unlike N2 purging, this approach can produce a CO2-rich stream after downstream steam condensation. The two-stage steam addition strategy achieved the highest CO2 capture capacity and showed stable performance over the tested cycles. These findings provide guidance for optimizing steam-assisted, energy-efficient CO2 capture systems in scalable CCUS applications.

ABSTRACT Li 4 SiO 4 ‐based sorbents are promising for high‐temperature post‐combustion CO 2 capture, but translating high‐performance laboratory powders into mechanically robust industrial pellets remains challenging. Herein, a K─Ti co‐doped Li 4 SiO 4 pellet sorbent was systematically optimized through powder‐stage dopant screening and pellet‐stage calcination engineering. Initially, a comparative study was conducted on powder sorbents co‐doped with K─Al and K─Ti. Results revealed that both Al and Ti were incorporated into the Li 4 SiO 4 framework, thereby optimizing the crystal microstructure and accelerating the reaction kinetics. Among the tested candidates, the K─Li 4 Si 0.95 Ti 0.05 O 4 delivered the highest CO 2 uptake capacity (0.31 g CO2 /g sorbent ) and rapid sorption kinetics under 15%–100% CO 2 . The optimal K─Ti formulation was then fabricated into millimeter‐scale pellets, followed by calcination optimization to balance chemical reactivity and mechanical strength. Physicochemical characterizations demonstrated that calcination at 800°C achieved a favorable equilibrium between chemisorption capability and structural stability. The optimized pellets exhibited high structural integrity, excellent cyclic stability, and sustained high mechanical crushing strength, reducing the risk of pulverization of high‐temperature sorbents. This work provides practical guidance for the microstructure design and powder‐to‐pellet fabrication of Li 4 SiO 4 ‐based sorbents for high‐temperature CO 2 capture, while further process‐level evaluation remains necessary before practical application.

Bimetallic oxygen carriers hold great promise for CH4 chemical looping reforming at 500-700 degrees C. Current research focuses on material optimization of lab-scale powders. However, industrial use requires mass production, shaping, and calcination-causing performance shifts from lab samples. Therefore, this study explored how beads-shaping and calcination affect a 10-kg-scale Fe-Ni oxygen carrier. Compared to powder, spheronized beads increased H-2 generation in reduction stage. Calcination at 1300 degrees C produced 2.5-time stronger beads than 1200 degrees C. Both calcined beads had 10-15 percentage points lower CH4 conversion at 550-600 degrees C, recovering to >92 % at 650 degrees C. The calcined beads produced 0.4-0.6 more H-2 from per CH4, though requiring more oxygen carrier input. Microscopical reasons to performance change were the shifts in reaction pathway and the forming of Fe-Ni-Al spinel. Macroscopical reasons were the oxygen release influenced by topology change. This work identifies key shaping and calcination parameters critical for oxygen carrier commercialization.

Chemical looping methane reforming (CLR) enables inherent C-H-O separation, making it a highly competitive route for low-carbon, low-cost hydrogen generation. FeNi composite oxygen carriers (OCs) are widely recognized as promising candidates; however, minimizing Ni usage is imperative to mitigate its inherent ecotoxicity and environmental risks without sacrificing CLR performance. Traditionally, such high performance has been attributed to the synergistic effects of a homogeneous, lattice-bonded FeNi spinel phase. This prevailing view is challenged by the fact that free NiO phase-separated from Fe2O3 (free NiO) can exhibit superior reactivity compared to its lattice-bonded counterpart, rendering it critical to decipher the trade-off between free and bonded NiO. Herein, a series of Fe2O3/NiO/Al2O3 OCs with tunable Ni-bonding ratios were synthesized and systematically evaluated at 550–650 °C. The totally-free NiO system achieved a maximum CH4 conversion of >95%. Crucially, a hybrid system with an optimized Ni-bonding ratio delivered the highest hydrogen yield (2.4–3.4 per CH4) while enabling a 25.0–62.5% reduction in NiO loading compared to conventional high-Ni counterparts. Mechanistic elucidation via temperature-programmed reduction, thermogravimetric analysis, and in-situ diffuse reflectance infrared Fourier transform spectroscopy revealed the distinct, cooperative roles of bonded and free NiO in activating CH bonds, regulating oxygen release, and steering the reaction pathway between complete and partial oxidation. This work provides a facile strategy to reduce Ni dosage in composite OCs, thereby mitigating the environmental footprint and improving the economic viability of CLR technology for clean energy transitions.

Solar-driven chemical looping dry reforming of methane (solar-driven CLDRM) aims at utilizing renewable energy for syngas production. In this study, Ni is incorporated in the pyrochlore-fluorite oxygen carriers (OCs) to reduce the temperature and enhance the performance of OCs. Experimental results show that the OC with 5 wt% Ni loading favors CLDRM at 700 degrees C, while LCNZ-10 wt% enables efficient solar-driven CLDRM at 600 degrees C. This demonstrates that Ni substitution with photo-response in the chemical looping process significantly reduces the reaction temperature compared to conventional catalytic DRM (900 degrees C). In addition, characterizations including XRD, Raman, XPS, UV-Vis, EIS, PL/TRPL, and TEM provide an overall perspective for understanding the effect of Ni particle dispersion on the stability, oxygen-ion conductivity, oxygen capacity, and redox cycling performance of OCs. The results demonstrate the potential of Ni-substituted pyrochlore-fluorite OCs in the application of solardriven CLDRM.

Sorption-enhanced chemical looping reforming (SE-CLR) integrates oxygen carrier redox cycling with in-situ CO2 capture to mitigate thermodynamic constraints and product inhibition for mid-temperature H-2 production. We develop the SE-CLR approach using particles (similar to 1.5 mm) of a trace-Cu-doped Fe-Ni/MgAl2O4 oxygen carrier and a Li4SiO4 sorbent co-promoted with K2CO3 and TiO2, operated in cyclic CH4 reduction-sorbent regeneration-air oxidation. At 600 degrees C, the approach achieved 78.2% CH4 conversion and an H-2 production rate of 4.37 mL g(-1) min(-1), while maintaining 92.3% CO2 capture efficiency and 87.6% H-2 purity. Continuous CO2 removal maintains a consistently low CO2 level throughout the reduction step and lowers the apparent activation energy from 34.182 to 20.126 kJ mol(-1). The sorbent retains a stable CO2 capacity of approximately 0.22 g CO2 g(-1) sorbent over 200 carbonation-decarbonation cycles. Quasi-in-situ XRD indicates a reversible Fe2O3 -> Fe3O4 -> FeO pathway without Fe-0 formation, while in-situ DRIFTS reveals CHx-derived species and carbonate/formate intermediates, evidencing rapid CO2 fixation and robust redox activity. The results demonstrate a promising mid-temperature SE-CLR approach for integrated H-2 production with inherent CO2 capture.

The growing demand for efficient high-temperature CO2 capture technologies is accelerating the search for durable and regenerable solid sorbents. Lithium orthosilicate (Li4SiO4) is a promising candidate due to its moderate regeneration temperature (<700 degrees C). However, traditional solid-state synthesis often results in severe particle sintering and poor cycling stability, while advanced wet-chemical approaches remain complex and costly. In this work, we propose a facile and scalable solid-state synthesis strategy that combines molten-salt promotion with hetero-element doping (Ti, Al, Fe, and Ce) to enhance the performance of Li4SiO4-based sorbents. Through systematic screening, Ti-doped Li4SiO4 (K-Li4Si0.95Ti0.05O4) emerged as the optimal composition, achieving a high CO2 uptake of 0.3 gCO2 gsorbent-1 and stable performance over 50 cycles. The selected sorbent was further processed into mechanically strong particles using a direct physical doping approach. The resulting K-Li4Si0.95Ti0.05O4 particles exhibited excellent CO2 sorption capacity (0.29 gCO2 gsorbent-1), rapid kinetics (0.2 gCO2 (gsorbent min)-1, long-term cycling stability over 100 cycles (0.28 gCO2 gsorbent-1) and sufficient mechanical strength (17 N). Mechanistic investigations using various in situ and ex situ characterization experiments revealed that Ti doping enhances performance through a synergistic mechanism by inducing lattice distortions to facilitate ionic migration and optimizing textural properties to promote CO2 diffusion. This work demonstrates that the facile, physically-doped solid-state route can deliver sorbents with performance on par with those made by wet-chemical methods, while retaining key advantages in simplicity, cost, and scalability, making them highly attractive for industrial-scale carbon capture applications.

The industrial deployment of Li4SiO4-based sorbents for high-temperature CO2 capture is often hindered by densification and diffusion limitations derived from particle shaping process. While K–Ti co-doping has been demonstrated to enhance intrinsic reactivity of Li4SiO4, balancing porosity with mechanical strength in shaped pellets remains a critical challenge. In this work, five porogen-templated K–Ti co-doped Li4SiO4 pellets were synthesized via extrusion–spheronization using typical porogens: α-cellulose fiber (CF), graphite (C), polyvinyl alcohol (PVA), and polyethylene (PE). The impact of diverse porogen on microstructural evolution, pore structure, and CO2 capture performances were systematically investigated through thermokinetic analysis and multi-scale characterization. Results indicate that the addition of porogen to Li4SiO4-based pellets increased the porosity of the pellets and enhance CO2 capture perfomance. The organic polymeric templates facilitate the formation of a highly interconnected mesoporous structure, yielding a significant increase in specific surface area compared to the porogen-free sample. Among these sorbents, CF- and PE-templated pellets demonstrated exceptional cyclic stability, maintaining a high capacity of > 0.25 gCO2/gsorbent over an extended 340 sorption–desorption cycle test. Notably, the CF-templated pellets successfully resolved the strength-kinetics trade-off by sustaining this capacity while exhibiting superior mechanical properties, including great compressive strength (15.9 N) and attrition resistance (< 5 wt

Hydrogen production is crucial for supporting the energy transition and achieving carbon neutrality goals. However, conventional natural gas steam reforming suffers from high temperatures, which lead to substantial exergy losses, promote carbon deposition, and compromise operational stability. Here, a mid-temperature (500-600 degrees C) chemical looping steam reforming (CLSR) process is proposed for efficient natural gas conversion. Fe-Ni oxygen carrier particles were developed by varying Fe/Al precursors, calcination temperatures, and powder sizes to achieve modulated physico-chemical properties. Systematic evaluation of chemical reactivity and physical indicators identified nm-Fe2O3-gamma-Al2O3 calcined at 1200 degrees C as the optimal formulation, combining high reactivity with a mechanical strength of 55.3 N. Reaction behavior was further investigated in a bench-scale packed-bed reactor with 100 g oxygen carrier loading. At 600 degrees C and a steam-to-carbon ratio of 1.5, the optimized process achieved over 85 % natural gas conversion and nearly 100 % ethane conversion, yielding a hydrogen production of 25 mL g(OC)(-1) and an H-2/CO ratio of 1.8. In addition, long-term stability tests confirmed that the oxygen carriers retained their oxygen transfer capacity and microstructure after 1000 isothermal redox cycles, while cold attrition tests showed a mass loss of only 0.73 % over 2 h. Furthermore, in-situ DRIFTs and XRD provided clear mechanistic insights into the CLSR process over Fe-Ni oxygen carriers, confirming the reaction pathway of natural gas activation and hydrogen production. Collectively, these findings highlight the promising performance of CLSR as an efficient route for low-carbon hydrogen production from natural gas.`.

The growing demand for efficient high-temperature CO 2 capture technologies is accelerating the search for durable and regenerable solid sorbents.

Piezocatalysis presents a sustainable and energy-efficient method for producing hydrogen (H2) and hydrogen peroxide (H2O2), utilizing mechanical energy to drive chemical reactions without the need for external power sources or harmful chemicals. In this study, we used a one-pot synthetic method to modify graphitic carbon nitride (g-C3N4). The obtained catalysts showed enhanced H2 and H2O2 production from pure water without any co-catalysts or sacrificial agents via piezocatalysis. In the cost-effective synthetic method, a metal oxide/g-C3N4 composite structure was constructed through the molten salt method. During thermal pyrolysis, non-noble metal-based SnCl2 provided a molten medium to facilitate the exfoliation of the g-C3N4 layer. The oxidation of SnCl2 and its interaction with g-C3N4 promoted the formation of g-C3N4/Sn-based composites. The synergistic interaction between exfoliated, defect-rich g-C3N4 and non-piezoelectrically active Sn species leads to a significant enhancement of the piezoelectric effect compared to pristine g-C3N4. Notably, the g-C3N4/Sn-based composites achieved superior H2 (3846.46 mu mol g-1 h-1) and H2O2 (999.11 mu mol g-1 h-1) production rates from pure water. This work provides new insights into the structural and compositional modulation of g-C3N4 without the use of any noble metals and paves the way for further piezocatalytic research using two-dimensional carbon nitride materials.

Ozone observations over oceanic areas remain inadequate or even non-existent in some areas, thus preventing the effective mitigation of the regional O3 pollution problem. Shipborne lidar measurements were conducted to investigate the distribution and transport of ozone over the southeastern coastal regions of China during the winter of 2024. The measurements were performed along the southeast coast of China from Zhejiang (ZJ) to Hong Kong (HK). Comparison of ozone concentration between ground-based observations and shipborne ozone lidar shows good agreement with each other, with a Pearson correlation coefficient (R) of 0.86. Spatial distributions of ozone concentration and transport flux are presented in combination with data assimilation. Two major transport pathways for pollution were found in the study area, including the northeastern path along the southeastern coast of China, and the southeast transport path. The analytical results for the distribution and transport of ozone show significant transport contributions to HK from the two major transport pathways just mentioned.

Sunlight-driven chemical looping dry reforming of methane (CLDRM) is a promising technology for solar fuel production with greenhouse gas utilization. Catalyst-assisted Ni/CeO2 oxygen carriers in different Ni loadings are used in thermal and light-driven CLDRM. The Ni nanoparticles effectively enhance the reactivity of methane dissociation, promote the oxygen release, and improve the light response of CeO2. The concentrated light significantly enhances the reactivity of CLDRM and suppresses carbon deposition by activating the reactants. At 600 degrees C, the oxygen carrier with moderate Ni loading (N5C) shows a 72.2 % increase in methane conversion and an 82.2 % increase in syngas yield under light illumination. The photoreaction exhibits superior stability over 50 redox cycles compared to the thermal reaction. Additionally, the CLDRM process is conducted under concentrated sunlight with 14.3 % solar-to-fuel efficiency and 7.3 mmol/g syngas production rate. This work provides a prospective approach for solar energy utilization and contributes to light-driven chemical looping applications.

Hydrogen-based direct reduction of iron oxides, particularly using renewable hydrogen sources, presents a sustainable, zero-carbon footprint alternative for the steel industry. However, the influence of secondary metallic elements on reduction pathways and the redox behavior of iron oxide remains insufficiently understood. In this study, we investigate the reduction and oxidation behaviors of NiFe2O4 and pure Fe3O4 using environmental transmission electron microscopy (ETEM), revealing that Ni incorporation fundamentally modifies the reaction pathway, simplifying the reduction process from a two-step to a single-step mechanism. Additionally, by examining the reduction processes of Ni-, Co-, Cu-, and Al-Fe3O4 systems, we demonstrate that secondary metals with appropriate oxide Gibbs free energy (ΔGoxide) and low mixing enthalpy (ΔHmix), such as Ni and Co, significantly accelerate reduction by promoting alloy formation and inhibiting oxidation. This work advances the understanding of iron oxide redox mechanisms and lays the groundwork for designing next-generation alloys and sustainable metallurgical strategies.

Dry reforming of methane (DRM) utilizes two major greenhouse gases, CO2 and CH4, to produce syngas (CO and H2), which is an important chemical intermediate resource for high-value chemicals synthesis. However, conventional DRM faces challenges such as catalyst deactivation, low product selectivity, and an unsuitable syngas ratio for downstream chemicals synthesis. To address these limitations, we propose a chemical looping dry reforming of methane (CLDRM) method, which achieves high methane conversion, superior syngas selectivity, and high-purity syngas for chemicals synthesis. In this study, 100 cycles of experiments were carried out using the LaFe0.8Al0.2O3 oxygen carrier. The results showed 88.3 % CH4 conversion, over 99 % CO selectivity, and a syngas yield of 8.1 mmol/g with an H2/CO ratio of 2 during the methane partial oxidation (POx) step. In the CO2 splitting step, the system achieved 81.3 % CO2 conversion with a CO yield of 2.6 mmol/g. The energy upgrade factor during the cycle reached 1.98. Furthermore, the performance of the proposed CLDRM-based chemicals production system was analyzed, taking acetic acid synthesis as a typical case. The new system achieved energy and exergy efficiencies of 62.9 % and 65.4 %, respectively, representing improvements of 11.5 % and 12.2 % compared to the conventional DRM system. Additionally, the new system reduced methane consumption by 8.84 % while increasing the CO2 fixation rate by 50.54 %. In summary, the proposed CLDRM process offers a promising pathway for CO2 reduction and cleaner utilization of CH4 for high-value chemicals production, supporting the transition to a more sustainable and low-carbon future.

Designing an efficient system for conversion of fossil fuel to hydrogen with lower environmental impact represents a promising strategy to meet the demands of a low-carbon future society. This study introduces an integrated chemical looping system combining hydrogen production and combustion for low-carbon fossil fuel conversion. The system achieves hydrogen production at 600 degrees C, significantly lower than conventional steam methane reforming (850 degrees C). Moreover, chemical looping combustion is employed to enable efficient CO2 capture. The proposed system is investigated from key reactions, system performance, and economic feasibility aspects. Experimental results show 80 % methane conversion, a hydrogen yield of 2.6 in the hydrogen production process, and nearly 100 % CO2 purity from purge gas combustion. Thermodynamic analysis reveals the energy and exergy efficiencies of 74.3 % and 68.9 %, surpassing the reference system by 3.6 % and 4.1 %, respectively. Economic assessment indicates a 10 % reduction in the levelized cost of hydrogen compared to the reference system. 1000 consecutive cycles confirm the outstanding stability of the oxygen carrier particles for the system. This study demonstrates the system's feasibility, cost-effectiveness, and potential for sustainable hydrogen production with minimal environmental impact, introducing a promising method for the efficient utilization of fossil fuels.

As a highly efficient and promising methane utilization technology, chemical looping dry reforming of methane (CLDRM) offers an environmentally friendly method for syngas production. The performance of the oxygen carriers (OCs) is determined by multiple properties such as thermal stability, oxygen-ion conductivity, oxygen capacity, and vacancies. In this study, a series of OCs were synthesized and characterized by adjusting the La3+/Ce3+ ratio at the A site of La x Ce2-x Zr2O7-delta. Experiments were conducted in a fixed-bed reactor to study the thermal properties of the OCs. Results showed that the LaCeZr2O7-delta pyrochlore with a La3+/Ce3+ ratio of 1:1 exhibited the highest H2 production (1.01 mmol g-1), CO selectivity (58.4%), and optimal H2/CO ratio (1.97). As the La3+/Ce3+ ratio decreases, a phase transformation was observed from pyrochlore (La2Zr2O7-delta) to the defective fluorite (Ce2Zr2O7-delta), as characterized by XRD, BET, Raman, TEM/HRTEM, STEM-EDS, XPS, and H2-TPR/O2-TPO. The microstructural evolution driven by the cation antisite, anion Frenkel disorder, and defect clustering correlates well with the performance of the pyrochlore-fluorite OCs, demonstrating an optimal balance between the thermal stability and high selectivity of the pyrochlore and the oxygen capacity of the defective fluorite. This result can be viewed as an alternative method for enhancing the clean hydrogen production in chemical looping dry reforming application.

Air pollution in China has shown significant improvement due to the strict implementation of emission control measures; however, pollution episodes caused by regional transport still occur frequently. This study investigates the three-dimensional distribution and transport mechanisms of PM2.5 in the Beijing-Tianjin-Hebei (BTH) region during the 2022 Beijing Winter Olympics, focusing on heavy pollution episodes before, during, and after the event. We integrated 34 LiDAR stations and surface monitoring data with six machine learning models (XGBoost, Random Forest, LightGBM, RNN, CNN-RNN, and CNN-BiLSTM) to reconstruct spatiotemporal PM2.5 dynamics. The CNN-BiLSTM model, with an R2 of 0.924, RMSE of 6.805 μg/m3, and MAE of 4.640 μg/m3, outperformed the others, benefiting from its dual capability to capture spatial and temporal dependencies. Based on the model results, distinct PM2.5 distribution patterns were identified across the three Olympic phases. During the pre-event period, high concentrations (∼180 μg/m3) were concentrated in the upper atmosphere (1 km above ground) south of BTH. In contrast, Beijing and Tianjin experienced near-surface pollution peaks during the event, likely driven by short-range transport. In the post-event phase, PM2.5 concentrations decreased overall, with pollutants transported southward under persistent northerly winds. Transport flux intensity (TFI) analysis highlighted key pollution pathways, with pre-event TFI peaking at 3.2 × 105 μg·m-1·s-1 in Beijing, event-phase TFI reaching 3.8 × 105 μg·m-1·s-1, and post-event TFI peaking at 7.8 × 105 μg·m-1·s-1. These findings underscore deep learning's role in PM2.5 inversion and reveal significant transregional pollution transport dynamics, offering insights for regional air quality management.

Chemical looping dry reforming of methane holds great promise for both CO2 utilization and syngas production with high efficiency. The structure and composition of oxygen carriers are critical factors influencing CL-DRM performance. Incorporating CeO2 is known to enhance the reactivity and stability of Fe2O3 in chemical looping reforming. However, the underlying mechanism of how CeO2 synergistically interact with Fe2O3 to enhance performances remains unclear. In this work, we comparatively investigated CeO2-supported Fe2O3 OCs in interfacial and physical Fe-Ce contact modes. We found the sol-gel-synthesized Fe2O3/CeO2 OC is in-situ activated within the first cycle and transforms to pure CeFeO3 through a strong Fe2O3-CeO2 interaction. The activated CeFeO3 achieves over 80% CH4 conversion, 96% CO selectivity, and excellent stability due to the sufficient Fe-Ce interaction, proper valence state, and low-energy barrier for oxygen diffusion. Additionally, in-situ environmental transmission electron microscopy study shows that the Fe2O3-CeO2 interaction promotes the oxygen release of both oxides during reduction. Under the oxidative conditions, iron exhibits significant activity to dissolve into the CeO2 lattice and form CeFeO3. The investigation into the activation mechanism of the Fe2O3/CeO2 material provides valuable insights for designing straightforward and cost-effective OCs.

Chemical looping steam methane reforming (CL-SMR) enables efficient hydrogen production with reduced irreversible losses. Oxygen carriers (OC) play a critical role in the overall performance of CL-SMR process. In this study, a new scheme for three-step CL-SMR process using NiFe2O4 OC is presented to accomplish cogeneration of syngas and high-purity hydrogen at a lower temperature range of 600 similar to 800 degrees C. Thermodynamic calculations demonstrate the temperature reduction potential in the proposed CL-SMR process, while establishing optimal conditions for hydrogen production. Fixed-bed experiments demonstrate 91.5 % of CH4 conversion, 485 mL g(-1) of total H-2 yield and 86.9 % of syngas yield ratio at 750 degrees C, with over 70 % H-2 purity of syngas and 79.8 mL g(-1) of pure hydrogen obtained in the reduction and oxidation step, respectively. The balance between carbon elimination and hydrogen production has been well settled. The phase transformation paths in each step of the CL-SMR process have been verified. The NiFe2O4 OC also exhibits satisfactory stability and oxygen capacity over 50 redox cycles. This study shows the capability of proposed CL-SMR to lower reaction temperature, maintaining superior performance for hydrogen production.