High Temperature CO2 Research Articles

Deactivated Ca-based sorbent derived from calcium looping CO2 capture as a partial substitute for cement to obtain low-carbon cementitious building materials

Calcium looping CO2 capture is a highly promising technology for carbon capture, utilization, and storage. Nevertheless, the disposal of deactivated calcium-based sorbents following cyclic carbonation and calcination processes presents an unresolved challenge. Concurrently, the development of low-carbon cement products is also a critical priority. Given the calcium-rich composition and carbon-negative nature of the calcium-based sorbent, it is proposed that the deactivated sorbent could be utilized as a partial substitute for cement in the production of building materials. This paper explored the potential of using two types of deactivated calcium sorbent (DPC/DGC) to partial substitute cement for low-carbon cementitious materials production. The effects of partial substitution of cement materials on volume stability, compressive/flexural strength, hydration kinetics, and carbon emission of the composite cementitious materials were investigated. The results indicate that a 5% and 10% replacement of cement with DPC/DGC has modest impact on volumetric stability and compressive strength. The composite cement with 5% DPC replacement achieves a 28-day compressive strength of 48.1MPa, representing a 0.4% increase compared to the 47.9MPa observed in the reference sample. Specimens with 15% DPC/DGC substitution exhibit inferior volume stability and mechanical performance than the control sample. The total hydration heat releases decrease with the increasing substitution ratio due to the dilution effect by the introduction of DPC/DGC. Additionally, substituting cement with Ca-based sorbents significantly reduced the carbon footprint of construction materials. The net carbon footprints for the building materials that containing 1 ton of binder (substitued with 10wt% DPC and DGC) were 152.5kg and 43.5kg, corresponding to reductions of 79.6% and 94.2% compared to reference cement mortar. These carbon footprints are projected to further decrease to -108.5kg and -375.5kg when DPC and DGC were obtained after 100 CO2 capture cycles. A novel technological route combining the high-temperature calcium looping CO2 capture and CO2 mineralization curing was proposed, and the associated challenges of this method were also discussed.

High temperature capture of CO2 on Li4SiO4 sorbents via a simple dry ball-milling coupled with K2CO3 physical addition

The reversible CO2 absorption/desorption of lithium orthosilicate (Li4SiO4) sorbents holds potential for high temperature capture of CO2 from hot flue gases, sorption-enhanced reforming and solar thermochemical energy storage. In this study, we have prepared a series of Li4SiO4 sorbents using a combination of K2CO3 addition and dry ball-milling procedure to improve the relatively slow kinetics under low CO2 partial pressure conditions. The synergistic effects of dry ball-milling and K2CO3 addition on the intrinsic properties of Li4SiO4 sorbents were explored by thermogravimetric analysis and structural characterizations. Thermogravimetric analysis indicate that the highest CO2 uptakes were achieved with dry ball-milling combined with K2CO3 physical addition. The structural characterizations further reveal that this sorbent (P-3K-1.5 M) had the smallest crystallite/particle size, largest surface area, and highest availability of surface alkaline-sites. The kinetics analysis also demonstrates that P-3K-1.5 M exhibited the fastest sorption kinetics during a double process. Additionally, P-3K-1.5 M maintained a high capacity over 10 sorption/desorption cycles. Therefore, this synthesis technique, which is simple, cost-effective, and easily scalable, shows great promise for high-temperature CO2 capture.

Hydrothermal-calcination synthesis of lithium orthosilicate microspheres for high-temperature CO2 capture

In recent years, the Li4SiO4 adsorbent has become a promising candidate for high-temperature CO2 capture. The fabrication of micro-structured Li4SiO4 could enhance the capture performance effectively. However, there exists a conflict between the purity and the morphology of prepared micro-structured Li4SiO4. This study proposed a novel hydrothermal-calcination method, which could produce Li4SiO4 microspheres with great morphology and relatively high purity. The physicochemical properties, CO2 capture performance and forming mechanisms of Li4SiO4 microspheres are evaluated and investigated systematically. It is found that the hydrothermal process could fabricate micro-spherical LiOH@Li2SiO3 precursor, which was further converted to Li4SiO4 microspheres during the subsequent calcination process. The LiOH@Li2SiO3 precursor could not only maintain the microstructure but also reduce the Li4SiO4 generation temperature, thus improving the morphology as well as the purity of obtained Li4SiO4 microspheres. As a result, the adsorbents could reach a CO2 capture capacity of 0.167–0.222 g/g within 30 min's adsorption under 15 vol.% CO2, and their cyclic stability are diverse depending on the used calcination temperatures. The hydrothermal-calcination contributes to the future preparation of high-performance Li4SiO4-based CO2 adsorbents.

Influence of oxygen partial pressure on the passivation and depassivation of super 13Cr stainless steel in high temperature and CO2 rich environment.

The passivation and depassivation characteristics of Super 13Cr stainless steel were examined under a range of oxygen partial pressures within a high-temperature (120 ℃) and high-pressure (3MPa) CO2 atmosphere. We performed comprehensive electrochemical assessments, encompassing open-circuit potential monitoring, electrochemical impedance spectroscopy, and linear polarization resistance analysis, to evaluate the corrosion resistance and passive film stability. The results demonstrate that the addition of low O2 partial pressures enhanced the stability of the passive film, while higher O2 levels led to the loss of the passivation properties of Super 13Cr stainless steel. The study elucidates the pivotal role of oxygen in the corrosion mechanisms affecting Super 13Cr stainless steel, presenting valuable data to enhance for integrity management in severe environmental conditions.

Corrosion Behavior of Newly Designed Fe-Ni-Base Alloys in High-Temperature CO2 at 700 °C

Corrosion Behavior of Newly Designed Fe-Ni-Base Alloys in High-Temperature CO2 at 700 °C

Experimental investigation on fracture propagation in shale fractured by high-temperature carbon dioxide

The productivity of shale reservoirs was significantly enhanced by the high-temperature CO2 fracturing technique. The injection of high-temperature CO2 into the formation induced rock fracture propagation, creating advantageous pathways for fluid flow. In this research, a self-developed in situ high-temperature convective heat simulation experimental apparatus was employed to systematically conduct simulated experiments on high-temperature CO2 fractured shale under different influencing factors. The experimental results demonstrated that the permeability of CO2 increased as the injection temperature increased. The rock fracture pressure was effectively reduced by high-temperature CO2 fractured shale. Higher complexity was observed in fracture propagation, accompanied by a substantial increase in microcracks and branching fractures. The shale fracture pressure increased with increasing triaxial stress and CO2 injection rate. The confining pressure restricted the further propagation of fractures under relatively high stress conditions, thereby reducing the width and density of fractures, lowering the fracture complexity. Nevertheless, the thermal shock effect of the fluid was exacerbated as the injection rate of high-temperature CO2 increased. The initiation of microcracks was facilitated by the intensification of local thermal stress in shale, inducing multiple curved fractures and forming a more complex fracture network. Compared to horizontal bedding shale, the fracture pressure of vertical bedding shale was relatively higher during high-temperature CO2 fracturing. In addition, the geometric morphology of fracture propagation was more complex, characterized by rougher fracture surfaces, leading to a greater improvement in reservoir reconstruction volume. This research contributed to the optimization of CO2 resource utilization, provided experimental evidence for the application of high-temperature convection fracturing technology in in situ shale conversion projects.

Unraveling the corrosion behavior and corrosion scale evolution of N80 steel in high-temperature CO2 environment: The role of flow regimes

During CO2 transportation and storage, metal equipment such as oilfield pipelines suffers from severe CO2 corrosion, especially in harsh downhole injection equipment. In this study, we investigated the corrosion behavior of oil well tubing in a high-temperature, high-pressure (HTHP) CO2-containing environment. The evolution of the corrosion scale was also examined under different flow regimes. The results reveal a lower corrosion rate at 150 °C compared to 80 °C under different flow regimes, with localized corrosion intensifying as temperature and rotational speeds (vrs) increase. The temperature also induces the corrosion scale conversion of aragonite-type CaCO3 (80 °C) to calcite-type CaCO3 (150 °C). Specifically, the variation of the corrosion rate and the corrosion scale evolution can be attributed to the vortices within the reactor. The intact vortex cells enhance mass transfer while also promoting nucleation and growth of CaCO3. However, when vrs exceeds the critical Reynolds number, the vortex cells are disrupted, resulting in viscous dissipation and a reduced corrosion rate.

Strong Metal-Support Interaction between Pt and TiO2 over High-temperature CO2 Hydrogenation.

The catalytic activities and stability of oxide-supported metal catalysts are significantly affected by metal-support interactions (MSI) between oxidic supports and supported metals. The surface properties of the support, such as its phase and defects, are crucial in MSI, including both the strong metal-support interaction (SMSI) and electronic metal-support interaction (EMSI). In this study, modulation of SMSI was achieved on rutile-supported Pt nanoparticles (NP) over high-temperature CO2 hydrogenation. The encapsulation of Pt NP surfaces with TiO2-x overlayers is precisely controlled by the defects. It is found that oxygen vacancy defects significantly enhance the catalytic stability of Pt/rutile under high-temperature reverse water-gas shift (RWGS) reaction by inhibiting the occurrence of SMSI. Pt/rutile with oxygen vacancies achieves a 301 molCO×gM-1×h-1 space time yield and considerably catalytic stability (decreased by 8%) at 800 °C over 100 h time-on-stream. Density functional theory (DFT) calculations suggest that the adsorption capacity of Pt NP on the rutile overlayer can be reduced by increasing electron density. Experimental results combined with DFT calculations show that electron transfer from Pt NP to rutile is reduced by the oxygen vacancy defects on Pt/R, preserving the metallic nature of Pt species during CO2 hydrogenation, thereby preventing the formation of SMSI.

Evaluation of calcium looping CO2 capture and thermochemical energy storage performances of different stabilizers promoted CaO-based composites derived from solid wastes

Calcium looping is considered as an important high-temperature cyclic CO2 capture and concentrated solar energy storage technology. However, the dramatic inactivation of CaO over multiple carbonation-calcination cycles has seriously restricted their practical applications. In this study, a series of metal oxide (i.e. TiO2, MgO, Al2O3 and ZrO2)-stabilized CaO-based materials with high cyclic stability derived from carbide slag were synthesized via a facile and cost-effective approach for simultaneously enhanced CO2 capture and thermochemical energy storage (TCES). The results suggest that CCS-H-TiO2 exhibits high initial CO2 uptake of 0.41 gCO2/gsorbent, superior cyclic stability with an average attenuation of 1.71 %/cycle and remarkably stable energy storage density. CCS-H-Al2O3 shows the best stability with lowest attenuation rate of 9.6 %. Except for CCS-H-MgO, the stabilizers reacted with active calcium to form new phases and used as physical “barrier” and high-TT skeleton to offset the sintering stress, retain the microporous structures, hinder the excessive agglomeration and alleviate sintering.

Organic Carbon and Ca‐Rich Carbonate Detections in Soils of the Northern Plains, Mars: Evaluation of Unreported Data From the Mars Phoenix Scout's Thermal Evolved Gas Analyzer (TEGA)

AbstractThe Thermal Evolved Gas Analyzer (TEGA) analysis of surface and icy subsurface Phoenix landing site soils consisted of low (300–700°C) and high (>700°C) temperature CO2 evolutions that were attributed to organic carbon (83–1,484 μgC/g) and Ca‐rich carbonate (1.1–2.6 wt.%). Total carbon abundances ranged from 1,143 to 4,905 µgC/g, which is the highest soil carbon concentration so far detected on Mars. Low temperature CO2 was attributed to oxidized organic C (e.g., oxalates, acetates), while hydrocarbon combustion was indicated in two soils by the detection of coevolved CO2 and O2 (perchlorate). Combustion reactions may have prevented the detection of hydrocarbon masses in the Phoenix landing site soils. Organic C was likely derived from meteoritic and igneous/hydrothermal sources, but microbiological sources cannot be excluded. CO2 evolved at high temperatures was consistent with Ca‐rich carbonate along with possible minor contributions from macromolecular organic carbon and mineral/glass vesicle CO2. Carbon detected in the Phoenix landing site soil and other landing site soils and sands (e.g., Gale/Jezero craters) would be consistent with global organic C and carbonate in soils and sand across Mars. However, oxidizing water thin films derived from the near‐surface ice in the Phoenix soils favor Ca‐carbonate over Fe‐carbonate, which is likely more stable in the ice‐free regions of Mars (e.g., Gale/Jezero craters). The global carbon budget on Mars inferred from these results emphasizes that Mars Sample Return should yield carbon bearing soil/rock that would allow the identification of the origin of carbon and any possible connections to ancient martian microbiology.

Simultaneous bulk and surface modifications of g-C3N4 via supercritical CO2-assisted post-treatment towards enhanced photocatalytic activity

A high-temperature supercritical CO2 (ScCO2)-assisted post-treatment strategy is developed to simultaneously modify the bulk and surface structures of graphitic carbon nitride (g-C3N4) using ScCO2 as penetrant and a small amount of methanol/acetonitrile mixture as modifiers. Specifically, the product of modified g-C3N4 is obtained through the post-treatment of pristine g-C3N4 in a homogeneous ScCO2/methanol/acetonitrile system, continuously heating to reach a target temperature (330 °C, 15.2 MPa) without a residence time. With the assistance of ScCO2, organic molecules penetrate the interlayers of g-C3N4 and subsequently modify the in-plane structure of g-C3N4. Methanol induces the partial transformation of g-C3N4 into a carbon nitride with a poly(heptazine imide)-like structure and with abundant methyl and hydroxyl groups. Simultaneously, acetonitrile polymerizes into 2,4,6-trimethyl-1,3,5-triazine, which is then covalently grafted onto the surface of modified g-C3N4. Remarkably, the entire post-treatment process is completed within 5 min, achieving a final product yield of 92.3 %. The modified g-C3N4 photocatalyst achieves an H2-evolution rate of 2126.1 μmol·h−1·g−1 and a CO2-to-CO conversion rate of 874.1 µmol·h−1·g−1. This work provides a green, efficient, high-yield, and scalable strategy for preparing layered and porous non-metallic photocatalysts using supercritical fluids technology.

Synthesis of highly stable Li4SiO4-based CO2 sorbents using polysilicon by-product SiCl4 as raw material

With the rapid development of the photovoltaic industry, the demand for polysilicon has been continuously increasing. In the production of polysilicon, a large amount of SiCl4 will inevitably be produced as a by-product. Proper treatment of this SiCl4 is crucial for reducing environmental pollution and controlling the production costs of polysilicon. In this study, a by-product of polysilicon production SiCl4 was utilized as a silicon source to synthesize the high-temperature CO2 sorbent Li4SiO4. The effects of SiCl4 content in the precursor solution and CO2 volume concentration on the adsorption performance of the sorbents were thoroughly investigated. The results showed that Li4SiO4-x (x = 0.5, 1.5, and 2.5) exhibited excellent adsorption performance and cyclic stability under 100 vol% CO2 atmosphere, with adsorption capacities of 26.29, 29.66, and 34.04 wt% after 15 cycles, respectively. Additionally, the study found that as the CO2 concentration decreased from 100 vol% to 50 vol% and 15 vol%, the adsorption equilibrium temperature showed a slight shift to the left, and the adsorption capacity also decreased to varying degrees, but the material maintained good cycle stability throughout the process. In summary, the synthesis of Li4SiO4 from SiCl4 has broad application prospects.

CeO2-confined Ni-Fe alloy enhanced high-temperature CO2 hydrogenation to CO

NiFe2O4 exhibits excellent redox properties and is widely applied in catalytic reactions. However, rapid inactivation under reaction conditions limited its industrial applications. In this study, CeO2-NiFe2O4 composite catalysts were synthesized, and the Reverse Water Gas Shift (RWGS) reaction was measured to reveal its CO2 hydrogenation performance under a high-temperature condition. NiFe2O4 catalysts got deactivated after being reduced to Fe-Ni alloy at 700 °C, decreasing the CO2 conversion rate. CeO2 addition can significantly improve its high-temperature activity, and 20CeO2-NiFe2O4 exhibited the best catalytic activity (80.85 %, 700 °C). The CeO2-confined maintained Ni-Fe alloy with a relatively small crystal size and larger specific surface area, supporting more active sites for CO2 hydrogenation. CeO2 addition induced higher oxygen vacancy concentration, enhancing CO2 activation and formates species formed on 20CeO2-NiFe2O4, resulting in higher CO2 conversion activity. In addition, 20CeO2-NiFe2O4 maintained its catalytic stability for 50 h at 700 °C. The CeO2 confined enhanced the high-temperature stability of Fe-Ni alloy. CeO2 and formed CeFeO3 dispersed in 20CeO2-NiFe2O4 inhibited excessive aggregation of Fe-Ni alloy, and CeO2 inhibited carbon deposition on Fe-Ni alloy, improving Fe-Ni alloy’s reaction stability under RWGS reaction conditions. CeO2 confined may give insight into improving metal stability under high-temperature and reductive conditions in heterogeneous catalysis.

Process simulation and techno-economic analysis of CO2 capture by coupling calcium looping with concentrated solar power in coal-fired power plant

The calcium looping (CaL) cycle is an effective high-temperature CO2 capture technology, its primary energy consumption arises from the calcination process, which limits the development of CaL technology. Utilizing concentrated solar power (CSP) instead of combustion for the calcination process in the CaL cycle can significantly reduce the energy penalty associated with CO2 capture of coal-fired power plants. Currently, the application of coupling CaL with concentrated solar power (CaL-CSP) systems in coal-fired power plants is still in its infancy, and there is limited research on its thermal performance and techno-economic analysis. In this study, a process simulation model of a 660 MW supercritical coal-fired power plant is developed as a reference. Subsequently, four different heat transfer routes are integrated into the design of CaL-CSP systems. The results indicate that the coupled power plant achieves a CO2 capture rate of 90 % compared to the reference coal-fired power plant, and reduces annual CO2 emissions by 93 % to only 58.2 g CO2/kWh. The CO2 capture energy penalty is 0.24 MJ/kg CO2. A sensitivity analysis of power generation cost reveals that if the cost of solar concentrator components is halved, the power generation cost will decrease to just 25 % higher than the reference power plant. Given the rapid advancements in CSP technology, this reduction is likely to be realized soon. Moreover, with the increase in carbon taxes and carbon prices, the power generation cost is expected to further decrease.

Preparation of nano-Al2O3 support CaO-based sorbent pellets by novel methods for high-temperature CO2 capture

CaO-based sorbents show great promise as materials for CO2 capture. In this paper, three novel preparation methods were proposed to prepare three sorbent pellets based on carbide slag, respectively. The CO2 cyclic capture performance of the sorbent pellets was also investigated. These three novel preparations consist of different binders (agar, gelatine) and different hydrophobic materials (silicone oil, liquid paraffin and silicone mold), respectively. The capture performance of these three sorbent pellets was compared with that of sorbent pellet prepared by existing preparation methods, which used agar as a binder and silicone oil as a hydrophobic material. In addition, the effects of the contents of nano-Al2O3 supports on the sorbent pellets were explored. Among the four preparation methods, the sorbent pellets prepared with agar as binder and silicone mold as hydrophobic material showed exhibiting the highest total capture capacity of 7.70 gCO2/g during 15 cyclic captures. The nano-Al2O3 was used as support to alleviate the sintering of the sorbent pellets prepared with agar as binder and silicone mold as hydrophobic material, preserving most of the CO2 diffusion channels. Among the sorbent pellets with varying contents of nano-Al2O3 support, the pellets with a 10:100 molar ratio of nano-Al2O3 to CaO demonstrated excellent mechanical properties and the highest CO2 cycle capture performance. These pellets exhibited a capture capacity of 0.626 gCO2/g on the first cycle, maintaining a capacity of 0.503 gCO2/g by the 15th cycle. This work introduced a novel method for preparing sorbent pellets of efficient and stable cyclic capture.

Enhancement effect of semicoke waste heat on energy conservation and hydrogen production from biomass gasification

Key approaches to alleviating global warming and curbing fossil fuel depletion involve various industrial energy-conservation technologies and carbon dioxide (CO2) emission reduction methods. The production of hydrogen (H2)-rich gas from inexpensive and readily available biomass, as an alternative energy source, is becoming increasingly promising. However, this application faces challenges such as high energy consumption and low gas quality. In this study, the waste heat released by semicoke production from lignite gasification and CO2 from exhaust gas were utilized to gasify biomass. This approach aims to save energy in biomass gasification and use CO2 in exhaust gas to improve the H2 content in biogas. A simulation was conducted to recover semicoke waste heat by combining a suspension tube with CO2 flow to generate steam and high-temperature CO2, which were then simultaneously sent into a gasifier to produce H2 through biomass gasification. The results revealed that the rate of semicoke waste heat recovery exceeded 90 %. The yield of steam and the rate of waste heat recovery improved with increasing mass flow rate of semicoke and then slightly decreased with increasing steam pressure and CO2 mass flow rate. The yield of H2 increased with the semicoke mass flow rate and steam pressure. The rate of energy conservation ranged from 15 % to 239 %, peaking at a CO2 mass flow rate of 0.09 kg/s. Compared with the case without waste heat recovery, the economic benefits increased from 12 to 28 times.

Evaluation of Na2CO3-doped MCM-48-Li4SiO4 adsorbent for CO2 capture: Performance and DFT mechanism

Efficient CO2 adsorbents are crucial for addressing the global climate crisis. In this study the novel adsorbents were synthesized using an impregnation precipitation method with MCM-48 as the silica source and Li2CO3 as the lithium source. By doping alkali metal carbonate (Na2CO3), the ML-Na2CO3 adsorbent was created for high-temperature CO2 capture. The results showed that the maximum adsorption capacity of 35.63 wt% was achieved at 600℃ in the mixture (15 vol% CO2, the balance being N2)when the adsorbent contained 15 wt% Na2CO3, representing a 4.49 wt% increase compared to the undoped ML adsorbent. The adsorption kinetics analysis confirmed a good fit with the biexponential model. Density Functional Theory (DFT) simulations revealed that the adsorption energy increased by an average of 0.1035 eV and Oslab exhibited high activity in chemisorbing CO2, forming CO32−. Na2CO3 doping modified the electronic structure of Oslab and Lislab, resulting in increased high-energy electrons, reflective activity, and improved CO2 adsorption energy. Overall, incorporating Na2CO3 enhanced carbon dioxide adsorption performance by 114.42 %, indicating a promising potential for real flue gas CO2 adsorption applications.

Modeling of Metal Matrix Concentrated Solar Receivers for sCO2 Power Blocks

Abstract Supercritical CO2 power blocks for Concentrating Solar Power (CSP) with novel metal matrix solar receivers have the potential to reduce operating expenses while improving overall system efficiencies. These concentrated solar receivers integrated with a metal matrix-based phase change (PCM) thermal storage medium provide the compounding effect of an efficient heat exchanger while also integrating thermal storage within the receiver. Detailed numerical modeling of such devices with enthalpy-porosity-based formulation for phase change and turbulent convective heat transfer for the sCO2 microchannels is described in the current work. With sCO2 power blocks operating at temperatures and pressures beyond 800°C and 200 bar, different high-temperature PCMs are studied. A detailed steady charging followed by discharge and charging transients is simulated to analyze the thermal performance of these devices. In the current work, the energy storage density of PCMs is studied, followed by an analysis of the movement of the melt-pool interface over the streamwise length of a high corrugation wavy microchannel. A scaling analysis is carried out to estimate the heat transfer coefficients while compare them with the numerical model predictions. The results from the current work can be utilized for sizing and detailed design of integrated solar receivers for high-temperature sCO2 power block applications.

A local acidic environment at the copper/molten salt interface enabling the efficient CO2 to CO conversion

The electrochemical reactions highly rely on the chemical environments, however, this phenomenon remains poorly understood in nonaqueous electrolyte. Herein, we study the effect of the electrode chemical environments on the electrochemical reduction of CO2 in molten carbonate. Using a Cu foam electrode, an acidic (CO2-rich) environment is created to achieve the efficient direct reduction of CO2 rather than the indirect reduction of CO32–. The acidic environment promotes a selective CO production thermodynamically, achieving a high CO current efficiency of 99 % at a current density of 779–1039 mA cm−2 at 700 °C. The Cu foam electrode works stably over 100 h at 260 mA cm−2 with an overpotential of 304 mV. This work reveals the role of the local chemical environment at the electrode/molten salt interface in governing the product selectivity and energy consumption, which is helpful for designing efficient high-temperature CO2 electrolyzers.

Encoding CO2 Adsorption in Sodium Zirconate by Neutron Diffraction.

Recent research into sodium zirconate as a high-temperature CO2 sorbent has been extensive, but detailed knowledge of the material's crystal structure during synthesis and carbon dioxide uptake remains limited. This study employs neutron diffraction (ND), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) to explore these aspects. An improved synthesis method, involving the pre-drying and ball milling of raw materials, produced pure samples with average crystal sizes of 37-48 nm in the monoclinic phase. However, using a slower heating rate (1 °C/min) decreased the purity. Despite this, the 1 °C/min rate resulted in the highest CO2 uptake capacity (4.32 mmol CO2/g Na2ZrO3) and CO2 sorption rate (0.0017 mmol CO2/g) after 5 min at 700 °C. This was attributed to a larger presence of microstructure defects that facilitate Na diffusion from the core to the shell of the particles. An ND analysis showed that the conversion of Na2ZrO3 was complete under the studied conditions and that CO2 concentration significantly impacts the rate of CO2 absorption. The TGA results indicated that the reaction rate during CO2 sorption remained steady until full conversion due to the absorptive nature of the chemisorption process. During the sorbent reforming step, ND revealed the disappearance of Na2O and ZrO2 as the zirconate phase reformed. However, trace amounts of Na2CO3 and ZrO2 remained after the cycles.