CO2-rich Atmosphere Research Articles

Properties of cement raw meals used as sorbents in a calcium looping process

Calcium looping (CaL) is a promising carbon capture and storage (CCS) technology that has the potential to significantly reduce CO2 emissions in cement production. Integrating CaL with cement production provides a viable solution to the high CO2 emissions generated during the calcination process. This study examines the behavior of two industrial cement raw meals from different sites (A-RM and B-RM) under CaL conditions, focusing on phase composition, particle size distribution, and clinker phase evolution up to 1450 °C. Calcination and CaL experiments were conducted in a CO2-rich atmosphere, with materials characterized using quantitative X-ray diffraction (Q-XRD) and high-temperature X-ray diffraction (HT-XRD). The results showed that both raw meals absorbed similar amounts of CO2 during the cyclic CaL experiments. A-RM formed C2S and other silicates, while B-RM retained more free CaO due to a less effective reaction with coarser quartz (SiO2) particles. HT-XRD revealed delayed clinker-phase evolution in the 1000–1400 °C range in CaL-treated raw meals. However, CaL-treated raw meals achieved low free CaO at 1450 °C, suggesting that optimal kiln conditions can produce the desired phase composition. These findings indicate that integrating CaL-treated raw meals into cement production requires careful optimization of operational parameters to maintain clinker quality and minimize energy consumption. Further research should focus on improving the efficiency and reactivity of CaL-treated raw meals to enhance their suitability for industrial cement production.

CO2 induced phase transition on a self-standing droplet studied by X-ray scattering and magnetic resonance

HypothesisAcoustic levitation is a suitable approach for studying processes occurring at the gas–liquid interfaces, as it allows its investigation in a contact-free manner while providing control over the gas phase. Here, we hypothesize that phase transitions induced by a CO2 rich atmosphere can be examined, at different length scales, in a contact-free manner. ExperimentalA system consisting of 12-hydroxysteric acid (HSA) soaps mixed with different ratios of monoethanolamine (MEA) and choline hydroxide, was prepared. Microliter droplets of the samples were acoustically levitated and monitored with a camera, while exposed to CO2 to modify the pH through diffusion at the air–liquid interface and inside the droplet. The phase transition and water mobility in the levitated droplets were evaluated through X-ray scattering (SAXS/WAXS) and magnetic resonance studies, in real-time. Finally, the droplets were collected and examined under the microscope. FindingsThe introduction of CO2 gas induced a phase transition from micelles to multi-lamellar tubes, resulting in a gel-like behavior both in the bulk and at the interface. The high stability of the acoustic levitator allowed the investigation of this dynamic phenomenon, in real-time, in a contact-free environment. This study showcases the suitability of acoustic levitation as a tool to investigate complex chemical processes at interfaces.

Collision-induced absorptions by pure CO2 in the infrared: New measurements in the 1150–4500 cm−1 spectral range and empirical modeling for applications

Knowledge of collision-induced absorptions (CIA) by pure CO2 for wide temperature ranges is necessary for atmospheric and climate studies of planets and exoplanets with CO2-rich atmospheres. In this work, using spectra measured with a Fourier transform spectrometer for temperatures between 230 K and 295 K at pressures up to 40 bar, several CIA bands in the 1150–4500 cm−1 spectral range have been determined, in some cases for the first time. The results are compared with values reported in the literature, showing good agreements. From data obtained in this work and those in the literature, we propose simple analytical models for the temperature dependent band shape and integrated band intensity (IBI) which enable the calculation of all investigated CIA transitions in a wide temperature range.

A-site alkali metal-doped SrTi0.3Fe0.7O3-δ: A highly stable symmetrical electrode material for solid oxide electrochemical cells

To addresses the limitations in electrode performance observed at temperatures ≤700 °C, attributed to the low oxygen surface exchange coefficient primarily caused by high Sr surface segregation, we developed an electrode performance enhancement strategy involving A-site alkali metal doping to SrTi1-xFexO3-δ (STF)-based perovskite. Here, we present the symmetrical electrode material for solid oxide electrochemical cells (SOCs), Sr0.95Mg0.05Ti0.3Fe0.7O3-δ (SMTF), demonstrating a unique combination of excellent symmetrical electrode performance and long-term stability. A-site Mg doping reduces the Sr surface segregation and improves the conductivity but also significantly enhances its electrochemical performance. At 700 °C, the performance of SMTF symmetric cell in both fuel cell and electrolysis modes is 1.5 times higher than that of STF. Moreover, under air atmosphere, SMTF demonstrates stable performance (>1000 h) at 1 A cm−2, with no degradation observed after 400 h testing under humidified hydrogen conditions. Additionally, SMTF exhibits excellent CO2 tolerance in CO2-rich atmospheres.

Assessment of carbonation as a complementary strategy to increase the durability of Magnesium Oxysulfate (MOS)-based fiber cement boards

Magnesium oxysulfate (MOS)-based fiber cement boards reinforced with lignocellulosic fibers were manufactured using the Hatschek process and cured for 24, 48, and 72 hours before curing in a CO2-rich atmosphere. The boards were rehydrated before the accelerated carbonation process to evaluate changes in carbonation after water addition to the system. The materials showed property changes after accelerated carbonation, which was responsible for an increase of approximately 15 % in the MOR values of the carbonated boards after 48 hours. In contrast, pre-rehydration of the boards increased the Modulus of Rupture (MOR), Limit of Proportionality (LOP), and Modulus of Elasticity (MOE)values of the carbonated materials and favored the production of cementitious composites with specific energy values close to 4.4 kJ/m2. The quantification of mineralized CO2 showed that the rehydrated and carbonated boards after 48 hours presented the highest SCO2(effective) values, which is related to the densification and consequent decrease in voids in the carbonated materials under these conditions. Accelerated aging showed that the carbonated boards had a lower loss of mechanical properties, demonstrating that accelerated carbonation, in addition to increasing mechanical properties, emerges as an alternative to increasing the long-term durability of MOS-based fiber cement boards.

Mechanical behaviour of sulphur-based Martian regolith concrete processed under CO2-rich conditions

Martian regolith holds promise as a potential construction material for future settlements on the planet's surface. However, the planet's predominantly CO2-rich atmosphere poses challenges that may impact the mechanical properties of regolith-based concrete materials. In this study, we explore the compressive and flexural characteristics of Martian regolith simulant concrete mixtures incorporating sulphur, processed under CO2-rich conditions. The results reveal that regolith simulant concrete mixtures containing 70 wt% sulphur exhibit a maximum flexural strength of 5.95 ± 0.25 MPa. Meanwhile, the highest compressive strength of 3.66 ± 0.25 MPa and elastic modulus of 9.57 ± 0.32 GPa are achieved with regolith simulant mixtures comprising 60 wt% sulphur. These findings offer crucial insights for the advancement of construction materials tailored for future Martian settlements.

Ion Velocity Map Imaging Study of the Reactive Collisions between Carbon Dioxide and Helium Ion.

The reactive collision between He+ and CO2 plays an important role in substance evolutions of the planetary CO2-rich atmosphere. Using a three-dimensional ion velocity map imaging technique, we investigate the low-energy ion-molecule reactions He+ + CO2 → He + CO2+/He + CO+ + O/He + CO + O+. The velocity images of the products CO+ and O+ of dissociative charge-exchange reactions are distinctly different from those of charge-exchange product CO2+. The remarkable features of stereodynamics are observed in the dissociative charge-exchange reaction and are attributed to the spatial alignment of the initially random target CO2 during the He+ approach. Branching ratios of different channels of dissociative charge exchange are further obtained with the Doppler kinematics model, indicating a high preference for the energy-resonant channel.

Green synthesis of ultra-long K2Ti4O9 whiskers via cornstarch foamed calcination for large scale application

A green synthesis approach of ultra-long K2Ti4O9 whiskers suitable for large-scale application via cornstarch foamed calcination was investigated. The addition of cornstarch forms well-defined ∼ 10 μm pores and a CO2-rich atmosphere to inhibit K2CO3 decomposition. The delayed decomposition generates high amounts of K2O melt which fosters the interface growth of whiskers with lengths up to 1 mm and high aspect ratios exceeding 5000. The resulting whiskers exhibit high crystallinity, meeting strict size requirements for various applications.

Evaporative cooling and reaction of carbon dioxide clusters by low-energy electron attachment.

Anionic carbonate CO3- has been found in interstellar space and the Martian atmosphere, but its production mechanism is in debate so far. To mimic the irradiation-induced reactions on icy micrograins in the Martian atmosphere and the icy shell of interstellar dust, here we report a laboratory investigation on the dissociative electron attachments to the molecular clusters of CO2. We find that anionic species (CO2)n-1O- and (CO2)n- (n = 2, 3, 4) are produced in the concerted reaction and further stabilized by the evaporative cooling after the electron attachment. We further propose a dynamics model to elucidate their competitive productions: the (CO2)n- yields survive substantially in the molecular evaporative cooling at the lower electron attachment energy, while the reactions leading to (CO2)n-1O- are favored at the higher attachment energy. This work provides new insights into physicochemical processes in CO2-rich atmospheres and interstellar space.

Effect of CO2-rich atmosphere on nitrogen configuration of char and bio-oil during nitrogen-rich pyrolysis of cellulose

Different volume ratios of carbon dioxide and nitrogen were mixed into the nitrogen-rich pyrolysis of cellulose, resulting in the production of nitrogen-doped biochar and nitrogen-containing bio-oil. When the urea mixture ratio was greater than 50%, the added CO2 promoted the production of nitrogen-containing bio-oil, reaching a maximum of 26.03% (M = 50%) at 10 vol% CO2 + 90 vol% N2. Pyridine, pyrrole, and amines were the main nitrogen-containing compounds produced when using atmospheres of pure nitrogen and carbon dioxide. Upon increasing the volume ratio of CO2, the nitrile content increased significantly, becoming one of the main nitrogen-containing compounds. In addition, due to chemical stability, the thermal conversion of CO2 demands a significant input of energy, so the required activation energy also increased. Adding CO2 to simulate high-temperature anoxic flue gas is a promising method for biomass pyrolysis to obtain nitrogen containing chemicals with high added value and high nitrogen doped Biochar.

The Importance of the Upper Atmosphere to CO/O2 Runaway on Habitable Planets Orbiting Low-mass Stars

Efforts to spectrally characterize the atmospheric compositions of temperate terrestrial exoplanets orbiting M dwarf stars with JWST are now underway. Key molecular targets of such searches include O2 and CO, which are potential indicators of life. Recently, it was proposed that CO2 photolysis generates abundant (≳0.1 bar) abiotic O2 and CO in the atmospheres of habitable M dwarf planets with CO2-rich atmospheres, constituting a strong false positive for O2 as a biosignature and further complicating efforts to use CO as a diagnostic of surface biology. Importantly, this implied that TRAPPIST-1e and TRAPPIST-1f, now under observation with JWST, would abiotically accumulate abundant O2 and CO, if habitable. Here, we use a multi-model approach to reexamine photochemical O2 and CO accumulation on planets orbiting M dwarf stars. We show that photochemical O2 remains a trace gas on habitable CO2-rich M dwarf planets, with earlier predictions of abundant O2 and CO due to an atmospheric model top that was too low to accurately resolve the unusually high CO2 photolysis peak on such worlds. Our work strengthens the case for O2 as a biosignature gas, and affirms the importance of CO as a diagnostic of photochemical O2 production. However, observationally relevant false-positive potential remains, especially for O2's photochemical product O3, and further work is required to confidently understand O2 and O3 as biosignature gases on M dwarf planets.

The Moon-Forming Impact and the Autotrophic Origin of Life.

The Moon-forming impact vaporized part of Earth's mantle, and turned the rest into a magma ocean, from which carbon dioxide degassed into the atmosphere, where it stayed until water rained out to form the oceans. The rain dissolved CO2 and made it available to react with transition metal catalysts in the Earth's crust so as to ultimately generate the organic compounds that form the backbone of microbial metabolism. The Moon-forming impact was key in building a planet with the capacity to generate life in that it converted carbon on Earth into a homogeneous and accessible substrate for organic synthesis. Today all ecosystems, without exception, depend upon primary producers, organisms that fix CO2 . According to theories of autotrophic origin, it has always been that way, because autotrophic theories posit that the first forms of life generated all the molecules needed to build a cell from CO2 , forging a direct line of continuity between Earth's initial CO2 -rich atmosphere and the first microorganisms. By modern accounts these were chemolithoautotrophic archaea and bacteria that initially colonized the crust and still inhabit that environment today.

Detectability of carbon with ChemCam LIBS: Distinguishing sample from Mars atmospheric carbon, and application to Gale crater

Onboard NASA's Curiosity rover, the ChemCam LIBS instrument has provided a wealth of information on the chemistry of rocks within Gale crater. Here, we use ChemCam in order to search for carbonates among the >3500 individual targets analyzed by this instrument. Because the carbon-lines are a combination of signal from the CO2-rich atmosphere and possible carbon from the targets, we developed a laboratory-based univariate calibration obtained under Mars-like atmosphere. We measured different type of carbon-bearing samples (sediments, coals, carbonates) and their mixture with a basaltic powder. Based on this work, the preferred approach to qualitatively assess carbon under a CO2-rich atmosphere is to use a ratio to an oxygen line (777 nm) and the estimated limit of detection for carbon in a single LIBS point are found to be of 4.5 wt% and 6.9 wt% for reduced and organic carbon, respectively. Considering carbonate, this LOD correspond to about 50 wt% carbonate in the analyzed volume.Analysis of data obtained on Mars by ChemCam up to sol 3350 reveals the presence of a correlation between the intensity of carbon and oxygen lines, as observed in the laboratory, confirming that most carbon signal is related to ionization of the atmosphere. Some variability in the carbon signal appears related to the physical state of the atmosphere (density, temperature).Based on a combined analysis of carbon lines and major element compositions (Ca, Fe, Mg), there was no detection of carbonate in the ChemCam dataset up to sol 3355. Therefore, we conclude that carbonate was not present as a major constituent (>50%) in the ChemCam LIBS targets, and that soils are not enriched in carbon beyond the limit of detection. The dominant salts present are sulfate, chlorides, and the lack of carbonates in Gale, while observed in Jezero, may at least partly be related to a difference in protolith.

Revised upper limits for abundances of NH3, HCN and HC3N in the Martian atmosphere

The Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft has been studying Mars' atmosphere since 2018. The sensitivity of the middle infrared channel (MIR) allows it to address many ardent topics and it is capable of improving and establishing upper limits for many trace species. In this work we present analysis of transmittance spectra in the 3332.5–3338.6 cm−1 range with 30,000 resolution (λ∕Δλ), covering absorptions lines of three nitrogen-bearing species: ammonia (NH3), hydrogen cyanide (HCN) and cyanoacetylene (HC3N). According to existing models, all of those are not expected to be present in a CO2-rich Martian atmosphere, but outgassing or unknown chemistry sources cannot be discounted. The upper limits of 14, 1.5 and 11 ppbv are obtained for NH3, HCN and HC3N from individual occultation measurements during the warm and dusty perihelion season of martian year 36. For the ammonia and hydrogen cyanide the upper limits are improved compared to previously published results. A search for cyanoacetylene on Mars is reported for the first time.

Experimental Analysis of the Effect of Cathodic CO2 Supply to Industrial Solid Oxide Fuel Cells

The integration of Solid Oxide Fuel Cells (SOFCs) in hybrid power generation systems offers the opportunity to achieve higher electric efficiencies. In the SOS-CO2 cycle [1], a newly developed cycle for blue power production (i.e., power generated starting from natural gas while capturing CO2), the SOFC cathode is supplied with mixtures of CO2 and O2, up to 79% CO2 molar fraction, while the anode is supplied with a reformate feed, containing H2, CH4, CO, CO2, and water vapour. Aim of this work is to experimentally evaluate the performance and the durability of industrial 5x5 cm2 Ni-YSZ anode-supported SOFCs under the SOS-CO2 cycle conditions, focusing on the effects of the CO2-rich cathodic atmosphere. The cells mounted a LSCF-based (La0.6Sr0.4Co0.2Fe0.8O3) single phase cathode, coated by a current collection layer of LSC (La0.6Sr0.4CoO3). Laboratory tests were performed at 700°C, acquiring polarization (I/V) curves and EIS spectra by means of a Horiba – FuelCon C50 Evaluator test station. Initial investigations with 7% humidified H2 and 21/79 O2/CO2 cathodic mixture revealed 25% power loss compared to the base case with cathodic air. The test showed not only that the loss of performance was stable in time, but also that the power reduction was reversible since the initial performance in air was recovered. The EIS spectra showed an increase of the polarization resistance and of the ohmic resistance upon feeding CO2. This latter observation suggested a reduction of the electronic conductivity of the cathode, compatible with the formation of Sr carbonates on the perovskite surface [2–4]. To assess the performance of the SOFC under the operating conditions of the SOS-CO2 cycle, the anode was supplied with reformate. Compared to the base case with humidified hydrogen and air, the current density at 0.7 V decreased by 37% (490 mA/cm2). When supplying the 21/79 O2/CO2 mixture at the cathode, the current density stabilized at 420 mA/cm2 (Figure 1). Durability tests (over 300 h) at 700°C with reformate and 21/79 O2/CO2 mixture highlighted a moderate decrease of the current density at 0.7 V. After these tests, the cathode was characterized post-mortem with XRD, SEM and Raman to analyse the consequences of the prolonged exposure to CO2. To further quantify the effect of CO2 on the cathode, symmetric button cells were also characterized with EIS, measuring ohmic and polarization resistances. The results suggested that the adsorption of CO2 is reversible and indicated a better suitability of LSCF- compared to LSC-based cathodes for operations with CO2-rich mixtures. Experiments performed between 550 and 700°C at varying CO2 and O2 partial pressures allowed to describe the kinetics of the oxygen reduction reaction and extract its activation energy. Overall, the results provided key elements for the integration of SOFCs in the SOS-CO2 blue power technology.

No thick carbon dioxide atmosphere on the rocky exoplanet TRAPPIST-1 c

Seven rocky planets orbit the nearby dwarf star TRAPPIST-1, providing a unique opportunity to search for atmospheres on small planets outside the Solar System1. Thanks to the recent launch of the James Webb Space Telescope (JWST), possible atmospheric constituents such as carbon dioxide (CO2) are now detectable2,3. Recent JWST observations of the innermost planet TRAPPIST-1 b showed that it is most probably a bare rock without any CO2 in its atmosphere4. Here we report the detection of thermal emission from the dayside of TRAPPIST-1 c with the Mid-Infrared Instrument (MIRI) on JWST at 15 µm. We measure a planet-to-star flux ratio of fp/f⁎ = 421 ± 94 parts per million (ppm), which corresponds to an inferred dayside brightness temperature of 380 ± 31 K. This high dayside temperature disfavours a thick, CO2-rich atmosphere on the planet. The data rule out cloud-free O2/CO2 mixtures with surface pressures ranging from 10 bar (with 10 ppm CO2) to 0.1 bar (pure CO2). A Venus-analogue atmosphere with sulfuric acid clouds is also disfavoured at 2.6σ confidence. Thinner atmospheres or bare-rock surfaces are consistent with our measured planet-to-star flux ratio. The absence of a thick, CO2-rich atmosphere on TRAPPIST-1 c suggests a relatively volatile-poor formation history, with less than {9.5}_{-2.3}^{+7.5} Earth oceans of water. If all planets in the system formed in the same way, this would indicate a limited reservoir of volatiles for the potentially habitable planets in the system.

Scaling laws for ablation waves formed by ice sublimation and rock dissolution: applications to the Earth, Mars and Pluto

Ablation waves involve solid substrate such as ice or soluble rocks. Ablation by sublimation or dissolution under turbulent winds or liquid flows may lead to the development of transverse linear bedforms (ablation waves) on volatile or soluble susbtrates. In glaciology, geomorphology, karstology and planetology, these ablation waves may provide relevant morphological markers to constrain the flows that control their formation. For that purpose, we describe a unified model, that couples mass transfers and turbulent flow dynamics and takes into account the relationship between the viscosity of the fluid and the diffusivity of the ablated material, for both sublimation and dissolution waves. From the stability analysis of the model, we derive three scaling laws that relate the wavelength, the migration velocity and the growth time of the waves to the physical characteristics (pressure, temperature, friction velocity, viscous length, ablation rate) of their environment through coefficients obtained numerically. The laws are validated on terrestrial examples and laboratory experiments of sublimation and dissolution waves. Then, these laws are plotted in specific charts for dissolution waves in liquid water, for sublimation waves in N2-rich atmospheres (e.g., Earth, Titan, Pluto) and in CO2-rich atmospheres (e.g., Mars, Venus). They are applied to rock dissolution on the walls of a limestone cave (Saint-Marcel d’Ardèche, France), to H2O ice sublimation on the North Polar Cap (Mars) and to CH4 ice sublimation in Sputnik Planitia (Pluto), to demonstrate how they can be used (1) either to derive physical conditions on planetary surfaces from observed geometric characteristics of ablation waves (2) or, conversely, to predict geometric characteristics of ablation waves from measured or inferred physical conditions on planetary surfaces. The migration of sublimation waves on regions of the Martian North Polar Cap and sublimation waves candidates on Pluto are discussed.

Measurements of sound propagation in Mars' lower atmosphere

Acoustics has become extraterrestrial and Mars provides a new natural laboratory for testing sound propagation models compared to those ones on Earth. Owing to the unique combination of a microphone and two sound sources, the Ingenuity helicopter and the SuperCam laser-induced sparks, the Mars 2020 Perseverance rover payload enables the in situ characterization of unique sound propagation properties of the low-pressure CO2-dominated Mars atmosphere. In this study, we show that atmospheric turbulence is responsible for a large variability in the sound amplitudes from laser-induced sparks. This variability follows the diurnal pattern of turbulence. In addition, acoustic measurements acquired over one Martian year reveal a variation of the sound intensity by a factor of 1.8 from a constant source due to the seasonal cycle of pressure and temperature that significantly modifies the acoustic impedance and shock-wave formation. Finally, we show that the evolution of the Ingenuity tones and laser spark amplitudes with distance is consistent with one of the existing sound absorption models, which is a key parameter for numerical simulations applied to geophysical experiments on CO2-rich atmospheres. Overall, these results demonstrate the potential of sound propagation to interrogate the Mars environment and will therefore help in the design of future acoustic-based experiments for Mars or other planetary atmospheres such as Venus and Titan.

Experimental Analysis of the Effect of Cathodic CO2 Supply to Industrial Solid Oxide Fuel Cells

In the SOS-CO2 cycle, a newly developed hybrid cycle for blue power production, the SOFC cathode is supplied with a CO2-rich oxidizing stream, while the anode is fed with a reformate mixture. The performance and the durability of 25 cm2 Ni-YSZ anode-supported SOFCs are experimentally evaluated under the SOS-CO2 cycle conditions for 150 h. By testing symmetric cells with LSCF-GDC and LSC-GDC electrodes, the effects of the CO2-rich atmosphere on the cathodic material are also investigated. The results show that the loss of performance caused by the cathodic supply of CO2 is stable in time, but also reversible when switching back to air. The cathodic supply of CO2 causes both an increase of the polarization resistance and of the ohmic resistance, suggesting a reduction of electronic conductivity compatible with formation of carbonates on the perovskite surface.

The advantage of praseodymium doped TiO2 composite as the support of Au catalysts for CO oxidation in CO2-rich atmosphere

In this study, based on the characteristic of lanthanide in oxygen storage capacity, a series of PraTibOx composite supports with different mole ratios of Pr to Ti and the corresponding Au catalysts were prepared - to investigate the oxidation of CO under CO2-rich atmosphere with lean oxygen content. A significant promotion in CO conversion rate over the catalyst with a molar ratio of Pr:Ti = 1:2 and a very high catalytic stability was also obtained. The addition of optimal Pr will make smaller gold particles, provide higher capacity in surface reactive oxygen releasing at low temperatures and weaken the deposition of carbonates in CO2-rich atmosphere. However, more Pr will strongly interact with gold, which leads to the majority of Au+ species in the catalysts and thus lower the catalytic activity. This study may provide a potential application of rare earth elements in sealed CO2-laser.