Search Results (27)

Carbon dioxide (CO₂) is the most significant anthropogenic greenhouse gas (GHG), accounting for approximately 81% of total emissions, with methane (CH₄), nitrous oxide (N₂O), and fluorinated gases contributing the remainder. Rising atmospheric CO₂ concentrations, driven primarily by fossil fuel combustion, industrial processes, and transportation, have surpassed the Earth’s natural sequestration capacity, intensifying climate change impacts. Carbon Capture, Utilization, and Storage (CCUS) offers a portfolio of solutions to mitigate these emissions, encompassing pre-combustion, post-combustion, oxy-fuel combustion, and direct air capture (DAC) technologies. This review synthesizes advancements in CO₂ capture materials including liquid absorbents (amines, amino acids, ionic liquids, hydroxides/carbonates), solid adsorbents (metal–organic frameworks, zeolites, carbon-based materials, metal oxides), hybrid sorbents, and emerging hydrogel-based systems and their integration with utilization and storage routes. Special emphasis is given to CO₂ mineralization using mine tailings, steel slag, fly ash, and bauxite residue, as well as biological mineralization employing carbonic anhydrase (CA) immobilized in hydrogels. The techno-economic performance of these pathways is compared, highlighting that while high-capacity sorbents offer scalability, hydrogels and biomineralization excel in low-temperature regeneration and integration with waste valorization. Challenges remain in cost reduction, material stability under industrial flue gas conditions, and integration with renewable energy systems. The review concludes that hybrid, cross-technology CCUS configurations combining complementary capture, utilization, and storage strategies will be essential to meeting 2030 and 2050 climate targets. Full article

High-temperature CaO-based CO₂ capture technology, energized by in situ coal combustion, exhibits substantial promise owing to its high energy efficiency, strong compatibility, and maturity. However, sorbent deactivation mechanisms under complex coal combustion conditions, particularly for industrially required pelletized sorbents, are unclear. Pelletized sorbents were co-fired with four representative coals (differing in Na-K, S, and Al-Si content) in this study. Key factors were decoupled, and two competing mechanisms were revealed: (1) High-temperature sintering deactivation: Single co-firing triggers localized overheating (>900 °C), causing severe sintering and pore collapse. This reduces the specific surface area by 29% and pore volume by 50%, occludes meso-/macropores, and leads to a significant drop in initial CO₂ capture capacity to 0.266–0.297 g/g. Coal types and minor residual surface impurities (<1.7%) are secondary factors. (2) Si-Al ash stabilization: During repeated co-firing (1–9 cycles), Si-Al ash components enrich on sorbents (0.1–7.6%), forming a thermally protective layer. After 20 adsorption–desorption cycles, the CO₂ capture capacity loss drops from 17.6% to 3.9%, improving cycle stability. These findings clarify these dual mechanisms, providing a theoretical basis for system optimization and highlighting precise control of the combustion temperature field as critical for industrial deployment. Full article

The urgent need to mitigate rising global CO₂ emissions demands the development of efficient carbon capture technologies. This study addresses the persistent challenge of sintering-induced performance degradation in CaO-based sorbents during high-temperature CO₂ capture. A novel solvent/nonsolvent synthetic strategy to fabricate CaO/CaAl-layered double oxide (LDO) composites was developed, where CaAl-LDO serves as a nanostructural stabilizer. The CaAl-LDO precursor enables atomic-level dispersion of components, which upon calcination forms a Ca₁₂Al₁₄O₃₃ “rigid scaffold” that spatially confines CaO nanoparticles and effectively mitigates sintering. Thermogravimetric analysis results demonstrate exceptional cyclic stability; the composite achieves an initial CO₂ uptake of 14.5 mmol/g (81.5% of theoretical capacity) and retains 87% of its capacity after 30 cycles. This performance significantly outperforms pure CaO and CaO/MgAl-LDO composites. Physicochemical characterization confirms that structural confinement preserves mesoporous channels, ensuring efficient CO₂ diffusion. This work establishes a scalable, instrumentally simple route to high-performance sorbents, offering an efficient solution for carbon capture in energy-intensive industries such as power generation and steel manufacturing. Full article

Although concentrated solar power (CSP) coupled with calcium looping (CaL) offers a promising avenue for efficient thermal chemical energy storage, calcium-based sorbents suffer from accelerated structural degradation and decreased CO₂ capture capacity during multiple cycles. This study used Density Functional Theory (DFT) calculations to investigate the mechanism by which Mg and Ni doping improves the adsorption/desorption performance of CaO. The DFT results indicate that Mg and Ni doping can effectively reduce the formation energy of oxygen vacancies on the CaO surface. Mg–Ni co-doping exhibits a significant synergistic effect, with the formation energy of oxygen vacancies reduced to 5.072 eV. Meanwhile, the O²⁻ diffusion energy barrier in the co-doped system was reduced to 2.692 eV, significantly improving the ion transport efficiency. In terms of CO₂ adsorption, Mg and Ni co-doping enhances the interaction between surface O atoms and CO₂, increasing the adsorption energy to −1.703 eV and forming a more stable CO₃²⁻ structure. For the desorption process, Mg and Ni co-doping restructured the CaCO₃ surface structure, reducing the CO₂ desorption energy barrier to 3.922 eV and significantly promoting carbonate decomposition. This work reveals, at the molecular level, how Mg and Ni doping optimizes adsorption–desorption in calcium-based materials, providing theoretical guidance for designing high-performance sorbents. Full article

Carbonation–calcination looping using CaO-based natural sorbents such as limestone is a promising technology for the capture of CO₂ from fossil fuel-based power plants. In this study, the CO₂ capture capacities of Buipe, Oterpkolu, and Nauli limestones from quarries in Ghana were measured in a laboratory-scale micro-fluidized bed reactor through multiple carbonation–calcination cycles. The changes in CO₂ capture capacity and conversion with the number of cycles mostly correlated with the changes in the physico-chemical properties: Capture capacity dropped from >60% to <15% after 15 cycles and the surface area dropped to below 5 m² g⁻¹ from as much as 20 m² g⁻¹ (for the Oterkpolu). The pore volume of the Nauli limestone was essentially invariant with the number of cycles while it increased for the Buipe limestone, and initially increased and then dropped for the Oterpkolu limestone. This decrease was likely due to sintering and a reduction in the number of micropores. The unusual increase in pore volume after multiple cycles was due to the formation of mesopores with smaller pore diameters. Full article

Using the combination of Concentrated solar power (CSP) and calcium looping (CaL) technology is an effective way to solve the problems of intermittent solar energy, but calcium-based materials are prone to sintering due to the densification of the surface structure during high-temperature cycling. In this study, the enhancement mechanism of Co and Cr doping in terms of the adsorption properties of CaO was investigated by Density Functional Theory (DFT) calculations. The results indicate that Co and Cr doping shortens the bond length between metal and oxygen atoms, enhances covalent bonding interactions, and reduces the oxygen vacancy formation energy. Meanwhile, the O²⁻ diffusion energy barrier decreased from 4.606 eV for CaO to 3.648 eV for Co-CaO and 2.854 eV for Cr-CaO, which promoted CO₂ adsorption kinetics. The CO₂ adsorption energy was significantly increased in terms of the absolute value, and a partial density of states (PDOS) analysis indicated that doping enhanced the C-O orbital hybridization strength. In addition, Ca₄O₄ cluster adsorption calculations indicated that the formation of stronger metal–oxygen bonds on the doped surface effectively inhibited particle migration and sintering. This work reveals the mechanisms of transition metal doping in optimizing the electronic structure of CaO and enhancing CO₂ adsorption performance and sintering resistance, which provides a theoretical basis for the design of efficient calcium-based sorbents. Full article

In this work, Aspen Plus was used to simulate a sorption-enhanced steam methane reforming (SE-SMR) process in a fluidized bed reformer using a Ni-based catalyst and CaO as a sorbent for CO₂ removal from the reaction environment. The performances of the process in terms of the outlet gas hydrogen purity (y_H2), methane conversion (X_CH4), and hydrogen yield (η_H2) were investigated. The process was simulated by varying the following different reformer operating parameters: pressure, temperature, steam/methane (S/C) feed ratio, and CaO/CH₄ feed ratio. A clear sorption-enhanced effect occurred, where CaO was fed to the reformer, compared with traditional SMR, resulting in improvements of y_H2, X_CH4, and η_H2. This effect, in percentage terms, was more relevant, as expected, in conditions where the traditional process was unfavorable at higher pressures. The presence of CaO could only partially balance the negative effect of a pressure increase. This partial compensation of the negative pressure effect demonstrated that the intensification process has the potential to produce blue hydrogen while allowing for less severe operating conditions. Indeed, when moving traditional SMR from 1 to 10 bar, an average decrease of y_H2, X, and η by −16%, −44%, and −41%, respectively, was recorded, while when moving from 1 bar SMR to 10 bar SE-SMR, y_H2 showed an increase of +20%, while X_CH4 and η_H2 still showed a decrease of −14% and −4%. Full article

This study investigates a novel approach to moderate-temperature carbon capture by examining the enhanced performance of thermally pre-treated dolomite. To obtain mixed oxides, dolomite samples were prepared via calcination in a quartz cylindrical furnace under an ambient atmosphere at 900 °C, and subsequently thermally pre-treated under an inert (argon) stream at 650 °C. Characterization of the as-prepared samples involved morphological, structural, textural, and optical features examined through XRD, BET, SEM-EDS, FT-IR, and RAMAN, XPS, and UV-vis spectroscopy, whereas TGA and subsequent multicyclic tests were used to study the CO₂ sorption. The dolomite sample calcined at 900 °C for 60 min, and after being activated under an inert atmosphere (argon), labeled PCD60Act, exhibited the highest CO₂ uptake of 0.477 g_CO2/g_sorbent; after 15 sorption–regeneration cycles, it still retained a CO₂ uptake of 0.38 g_CO2/g_sorbent at 650 °C, and it was also successfully regenerated at this moderate temperature, demonstrating 84% capture capacity retention. These remarkable results are explained by the crystalline defects generated during the thermal pre-treatments of the dolomite. This research offers valuable perspectives on the viability of employing thermally pre-treated dolomite as an inexpensive, thermally stable, and moderate-temperature regenerable CaO-based sorbent for applications in CO₂ removal in the context of integrated carbon capture and conversion (ICCC) for the production of high-purity hydrogen. Full article

Sorbents for CO₂ capture based on CaO have been synthesized and tested for sorption-enhanced steam reforming (SESR) via the co-precipitation method. Various stoichiometries of MgO and CeO₂ have been utilized along with Cao and an optimum stoichiometry was identified providing the highest capacity and stability over cycling. The as-synthesized sorbents were structurally characterized by means of XRD and SEM. The thermal characterization was obtained via TGA. The porosity of the synthesized samples was measured by the N₂ adsorption and mercury porosimetry. Based on the outcomes of the current work, the sorbents with the highest capacities presented a highly porous structure with a porosity level higher than 65%. The sorbents were tested at high temperatures over repeated cycling (carbonation/decarbonation) to identify the stability of the synthesized sorbents over cycling. The results showed that the stoichiometry of 6:2:1 (CaO, MgO, CeO₂) could retain a capacity up to 25 wt% even after 45 cycles. Full article

A promising solution for efficient methane (CH₄) storage and transport is a metal–organic framework (MOF)-based sorbent. Hence, searching for potential MOFs like M₂(BDC)₂(DABCO) to enhance the CH₄ storage capacity in both gravimetric and volumetric uptakes is essential. Herein, we systematically elucidate the adsorption of CH₄ in M₂(BDC)₂(DABCO) or M(DABCO) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn) MOFs using multiscale simulations that combined grand canonical Monte Carlo simulation with van der Waals density functional (vdW-DF) calculation. We find that, in the M(DABCO) series, Mg(DABCO) has the highest total CH₄ adsorption capacities, with $m_{tot}=$ 231.39 mg/g at 298 K, for gravimetric uptake, and $V_{tot}=$ 231.43 cc(STP)/cc, for volumetric uptake. The effects of temperature, pressure, and metal substitution on enhancing CH₄ storage are evaluated, and we predict that the volumetric CH₄ storage capacity on M(DABCO) could meet the DOE target at temperatures of ca. 238 K–268 K and pressures of 35–100 bar. The interactions between CH₄ and M(DABCO) are dominated by the vdW interactions, as shown by the vdW-DF calculations. The Mg, Mn, Fe, Co, and Ni substitutions in M(DABCO) result in a stronger interaction and thus, a higher CH₄ storage capacity, at higher pressures for Mg, Mn, Ni, and Co and at lower pressures for Fe. This work may provide guidance for the rational design of CH₄ storage in M₂(BDC)₂(DABCO) MOFs. Full article

CO₂ uptake by MgO-based sorbents at intermediate temperatures is attractive for pre- and post-combustion CO₂ capture applications. However, besides the high CO₂ uptake potential of these materials (1.1 g CO₂ g⁻¹ sorbent), in practice, the realistic CO₂ capture is far from that of the theorical values. In this work, the sol–gel method was used to synthetize unsupported and supported MgO sorbents (10% Ca⁻ or 10% Ce⁻ support, mol) that were impregnated with different fractions (15, 25, and 35; % mol) of a NaNO₃ single salt or a ternary alkali salt (NaNO₃, LiNO₃ and KNO₃ (18/30/52; % mol)). To understand the role of alkali metal salts (AMSs) in the MgO sorbents’ performance, the working and decomposition temperature ranges of AMS under different atmospheres (CO₂ and air) were evaluated. The findings show that the CO₂ uptake temperature range and maximum uptake (20–500 °C, CO₂ atmosphere) of sorbents are correlated. The cyclic CO₂ uptake of the most promising sorbents was tested along five carbonation–calcination cycles. For the first and fifth cycles, respectively, the 15 (Na, K, Li)-MgO sorbents showed the highest carrying capacity, i.e., 460–330 mg CO₂ g⁻¹ sorbent, while for the 15 (Na, K, Li)-MgO-Ca sorbents, it was 375–275 mg CO₂ g⁻¹. However, after the first cycle, the carbonation occurred faster for the 15 (Na, K, Li)-MgO-Ca sorbents, meaning that it can be a path to overpassing carbonation kinetics limitations of the MgO sorbent, making it viable for industrial applications. Full article

This article presents the results of research on magnesites from the Polish deposits of Szklary, Wiry and Braszowice as SO₂ sorbents under the conditions of fluidized bed combustion technology. In practice, magnesites are not used as SO₂ sorbents, and the role of magnesium in the desulfurization process under the conditions of fluidized bed combustion technology is evaluated differently among researchers. The literature data question the participation of magnesium in the process of SO₂ capture from flue gas and prove its high reactivity. Similarly, previous studies referred to the problem of the stability of magnesium-containing desulfurization products under high temperature conditions. This paper analyzes the SO₂ binding process and determines the parameters of the sorbent responsible for the efficiency of magnesite sorption. It was shown that MgO, formed as a result of thermal dissociation of magnesite, actively participates in the SO₂ binding reaction to form magnesium sulfate phases (MgSO₄ and CaMg₂(SO₄)₃) stable in the temperature conditions of fluidized bed boilers. The problem of differentiated reactivity of magnesium-containing sorbents should be associated with the porosity of the sorbents. If the secondary surface of the sorbent is developed based on micropores and smaller mesopores (below 0.1 µm), the sorbent will be characterized by low sorption activity. It was shown that the SO₂ binding process is then limited only to the outer part of the sorbent grains. This results in the formation of a massive, SO₂-impermeable desulfurization-product layer on the sorbent grain surface. In real conditions, where the reactions of CaCO₃ thermal dissociation and SO₂ sorption occur almost simultaneously, the inside of the sorbent grains may remain undissociated. The results of experimental research allowed us to trace the dynamics of the SO₂ binding process in relation to real conditions prevailing in fluidized bed boilers. Full article

Although copper is needed for living organisms at low concentrations, it is one of the pollutants that should be monitored along with other heavy metals. A novel and sustainable composite mineralizing sorbent based on MgO-CaO-Al₂O₃-SiO₂-CO₂ with nanosized adsorption centers was synthesized using natural calcium–magnesium carbonates and clay aluminosilicates for copper sorption. An organometallic modifier was added as a temporary binder and a source of inovalent ions participating in the reactions of defect formation and activated sintering. The sorbent-mineralizer samples of specified composition and properties showed irreversible sorption of Cu²⁺ ions by the ion exchange reactions Ca²⁺ ↔ Cu²⁺ and Mg²⁺ ↔ Cu²⁺. The topochemical reactions of the ion exchange 2OH⁻ → CO₃²⁻, 2OH⁻ → SO₄²⁻ and CO₃²⁻ → SO₄²⁻ occurred at the surface with formation of the mixed calcium–copper carbonates and sulfates structurally connected with aluminosilicate matrix. The reverse migration of ions to the environment is blocked by the subsequent mineralization of the newly formed interconnected aluminosilicate and carbonate structures. Full article

This study investigated the effect of HCl in biomass gasification producer gas on the CO₂ capture efficiency and contaminants removal efficiency by CaO-Fe₂O₃ based sorbent material in the calcium looping process. Experiments were conducted in a fixed bed reactor to capture CO₂ from the producer gas with the combined contaminants of HCl at 200 ppmv, H₂S at 230 ppmv, and NH₃ at 2300 ppmv. The results show that with presence of HCl in the feeding gas, sorbent reactivity for CO₂ capture and contaminants removal was enhanced. The maximum CO₂ capture was achieved at carbonation temperatures of 680 °C, with efficiencies of 93%, 92%, and 87%, respectively, for three carbonation-calcination cycles. At this carbonation temperature, the average contaminant removal efficiencies were 92.7% for HCl, 99% for NH₃, and 94.7% for H₂S. The outlet contaminant concentrations during the calcination process were also examined which is useful for CO₂ reuse. The pore structure change of the used sorbent material suggests that the HCl in the feeding gas contributes to high CO₂ capture efficiency and contaminants removal simultaneously. Full article

The effect of cyclic carbonation–decarbonation operating parameters on Zr-doped CaO sorbent CO₂ uptake capacity evolution is examined. It is revealed that the capacity steady state value increases with the decrease in the carbonation temperature, CO₂ concentration in the gas flow upon carbonation and with the increase in the heating rate from the carbonation to the decarbonation stages. The rise in decarbonation temperature leads to a dramatic decrease in the sorbent performance. It is found that if carbonation occurs at 630 °C in the gas flow containing 15 vol.% CO₂ and decarbonation is carried out at 742 °C, the sorbent shows the highest values of the initial and steady state CO₂ uptake capacity, namely, 10.7 mmol/g and 9.4 mmol/g, respectively. Full article