CO2 Capture Performance Research Articles

Preparation and CO2 capture performances of KIT-6@reduced graphene oxide composites

Preparation and CO2 capture performances of KIT-6@reduced graphene oxide composites

Thermodynamic simulation and experimental investigation of manganese oxide (MnOx) for integrated CO2 capture and conversion via chemical looping route

Due to its high energy conversion efficiency, low economic cost and collaborative pollution control, chemical looping is emerging as a promising technology to deal with CO2 emissions in energy and environmental fields. Based on the dual property of being carbonated and oxidized of MnO, the integrated CO2 capture and conversion performance of manganese oxide is analyzed via chemical looping CH4-O2-CO2 route. Thermodynamic calculation and process simulation indicate the equilibrium reduced solid is MnO instead of metallic Mn, which is consistent with material characterization. The gaseous oxygen released by MnO2 is the prerequisite for its reactivity from thermodynamic analysis and is the effective step for MnO2-CH4 reforming experiments. The CH4 reforming performance of Mn2O3 is limited from thermodynamic hierarchy and the lattice oxygen capacity of Mn3O4 affects its reactivity with CH4. Mn2O3 obtains the best partial oxidation reforming selectivity under higher operating temperature. The lattice oxygen is replenished with an obtained mole ratio of MnO2:Mn2O3 as 0.12:0.03 through air oxidation under medium temperature conditions. The weight increment at CO2 atmosphere indicates the 41.6 mol.% CO2 capture ability of MnO. The CH4-O2-CO2 cycle experiment proves the achievement in realizing the integrated CO2 capture and utilization with one material via chemical looping route.

One-step fabrication of size-controllable, biowaste-templated Li4SiO4 spherical pellets via freeze-drying method for cyclic CO2 capture

High-temperature cyclic CO2 capture based on Li4SiO4 adsorbent has drawn extensive attentions in recent decades. Especially, the fabrication of Li4SiO4 adsorbent pellets with sufficient mechanical strength has been considered as an essential precondition for achieving its practical looping application. In this work, size-controllable Li4SiO4 spherical pellets were one-step fabricated via a novel freeze-drying method. And a typical industrial biowaste, bagasse, was employed as a low-cost and carbon–neutral pore-forming agent to enhance the CO2 capture performance of freeze-dried Li4SiO4 pellets. It is investigated that as the increasing of liquid-to-solid ratio, the diameter of pellets gradually decreases from 2.3 mm to 0.9 mm and the interior structure becomes dense and nonporous, resulting in the inhibition of CO2 capture capacity and the enhancement of mechanical strength. As a result, the LP2.5 exhibit a capacity of 0.15–0.17 g CO2/g adsorbent while that of LP7.5 decreases to only 0.07 g/g. To compensate this capacity decline, the biowaste bagasse was further acted as the pore-forming agent to improve the porosity and structure of LP 7.5 pellets, leading to an effective capacity promotion of 0.04–0.06 g/g. Meanwhile, however, it also leads to a slight decline of mechanical strength. All of above conclusions contribute to the future development and practical applications of Li4SiO4 adsorbent pellets.

Mesoporous carbon nitride supported MgO for enhanced CO2 capture

The growing concern about the environmental consequences of anthropogenic CO2 emissions significantly stimulated the research of low-cost, efficient, and recyclable solid adsorbents for CO2 capture. In this work, a series of MgO-supported mesoporous carbon nitride adsorbents with different MgO contents (xMgO/MCN) was prepared using a facile process. The obtained materials were tested for CO2 capture from 10 vol% CO2 mixture gas with N2 using a fixed bed adsorber at atmospheric pressure. At 25 ºC, the bare MCN support and unsupported MgO samples demonstrated CO2 capture capacities of 0.99, and 0.74 mmol g−1, respectively, which were lower than those of the xMgO/MCN composites.The incorporation of MgO into the MCN improved the CO2 uptake, and the 20MgO/MCN exhibited the highest CO2 capture capacity of 1.15 mmol g−1 at 25 °C. The improved performance of the 20MgO/MCN nanohybrid can be possibly assigned to the presence of high content of highly dispersed MgO NPs along with its improved textural properties in terms of high specific surface area (215 m2g−1), large pore volume (0.22 cm3g−1), and abundant mesoporous structure. The efffects of temperature and CO2 flow rate were also investigated on the CO2 capture performance of 20MgO/MCN. Temperature was found to have a negative influence on the CO2 capture capacity of the 20MgO/MCN, which decreased from 1.15 to 0.65 mmol g−1with temperature rise from 25 C to 150º C, due to the endothermicity of the process. Similarly, the capture capacity decreased from 1.15 to 0.54 mmol g−1 with the increase of the flow rate from 50 to 200 ml minute−1 respectively. Importantly, 20MgO/MCN showed excellent reusability with consistent CO2 capture capacity over five sequential sorption–desorption cycles, suggesting its suitability for the practical capture of CO2.

Efficient CO2 Capture under Humid Conditions on a Novel Amide-Functionalized Fe-soc Metal-Organic Framework.

CO2 is the main source of the greenhouse gases, and its capture from flue gas under humid conditions is challenging but important for promoting carbon neutrality. Herein, we report a novel soc topology Fe-based metal-organic framework (Fe-dbai) with highly efficient postcombusion CO2 capture performance by integrating multiple specific functionalities, such as unsaturated metal sites and amide functional groups. The CO2 adsorption capacity and CO2/N2 selectivity of Fe-dbai are high up to 6.4 mmol/g and 64 (298 K, 1 bar), respectively, superior to many other reported MOFs. More importantly, the CO2 working capacity of Fe-dbai under 60% RH conditions preserves 94% of that under dry conditions in the breakthrough experiments of CO2/N2 (15:85, v/v) mixtures. The molecular simulation highlights that the electronegative amide CO- group has a good affinity for CO2 and can improve the interaction between Fe UMS and CO2. Although H2O molecules will occupy a small fraction of the adsorption sites, the confinement effect it produces can enhance the adsorption affinity of the framework for CO2, which results in Fe-dbai retaining most of the CO2 adsorption capacity under humid conditions. The excellent CO2 capture performance makes Fe-dbai a potential candidate for the practical application of CO2 capture.

Enhanced Carbon Dioxide Capture Using a Mixed Amino Acid Salt Solution

This study investigated the carbon dioxide (CO2) absorption and desorption performance of a mixed amino acid solution (containing glycine (G), alanine (A), proline (P), and lysine (L), GAPL). These four amino acids were intentionally selected to reflect the chemical and structural variations (pKa and steric hindrance of amino groups) of amino acids. The single cycle CO2 capture experiment showed that the GAPL salt solution had 19% higher CO2 absorption (0.91 mol CO2/mol amino acids) compared to the absorption calculated by adding the proportional capacities of G, A, P, and L (0.77 mol CO2/mol amino acids). 13C NMR data delineated the effects of individual amino acids on carbamate and bicarbonate/carbonate formation and elucidated the distribution of captured CO2 in the GAPL salt solution. The recirculation experiment concluded that the GAPL salt solution had much better CO2 capture performance than the conventional monoethanolamine process. Less than 10% of the absorption and cyclic capacity of the GAPL salt solution was lost after ten cycles of CO2 capture. This study demonstrated an approach that blended amino acid solutions can be tailored and designed as new, efficient reagents to massively capture CO2 in a technically feasible, economically viable, and environmentally friendly manner.

One-Pot Synthesis of Melamine Formaldehyde Resin-Derived N-Doped Porous Carbon for CO2 Capture Application

The design and synthesis of porous carbons for CO2 adsorption have attracted tremendous interest owing to the ever-soaring concerns regarding climate change and global warming. Herein, for the first time, nitrogen-rich porous carbon was prepared with chemical activation (KOH) of commercial melamine formaldehyde resin (MF) in a single step. It has been shown that the porosity parameters of the as-prepared carbons were successfully tuned by controlling the activating temperature and adjusting the amount of KOH. Thus, as-prepared N-rich porous carbon shows a large surface area of 1658 m2/g and a high N content of 16.07 wt%. Benefiting from the unique physical and textural features, the optimal sample depicted a CO2 uptake of up to 4.95 and 3.30 mmol/g at 0 and 25 °C under 1 bar of pressure. More importantly, as-prepared adsorbents show great CO2 selectivity over N2 and outstanding recyclability, which was prominently important for CO2 capture from the flue gases in practical application. An in-depth analysis illustrated that the synergetic effect of textural properties and surface nitrogen decoration mainly determined the CO2 capture performance. However, the textural properties of carbons play a more important role than surface functionalities in deciding CO2 uptake. In view of cost-effective synthesis, outstanding textural activity, and the high adsorption capacity together with good selectivity, this advanced approach becomes valid and convenient in fabricating a unique highly efficient N-rich carbon adsorbent for CO2 uptake and separation from flue gases.

Potassium citrate-derived porous carbon with high CO2 capture and Congo red adsorption performance

The objective is to achieve the goal of carbon neutrality, controlling CO2 emissions is a primary problem to be solved in the current environmental protection field. Eliminating the environmental pollution of dyes in industrial wastewater is also an urgent problem to be solved in the field of environmental protection. The adsorption technique is an effective way to deal with these two issues. Developing high-efficiency adsorbents is an essential work in the adsorption field. In this work, a simple carbonization method has been developed to prepare porous carbon. The morphology and structure of the prepared porous carbon were investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and surface area measurement. By studying the influence of preparation conditions on the structure and properties of the prepared carbon materials, it was found that the carbon materials prepared at 900 ℃ (PCMCA-900) exhibited a high specific surface area of 1476 m2 g−1 and a high total pore volume of 0.951 cm3 g−1. The PCMCA-900 showed the highest CO2 uptake of 7.67 mmol g−1 at 0 ºC and the adsorption capacity of PCMCA-900 decreased by less than 5% after 10 times recycling. Moreover, when PCMCA-900 was used as an adsorbent to remove Congo red in water, an adsorption capacity of 652.3 mg g−1 was achieved. Therefore, potassium citrate-derived porous carbon is a desirable candidate for excellent CO2 adsorption and Congo red in industrial wastewater.

Preparation, Characterization and Experimental Investigation of the Separation Performance of a Novel CaO‐based CO2 Sorbent for Direct Air Capture

AbstractThe capture of CO2 from air via direct air capture (DAC) is a promising way to reduce the carbon dioxide concentration in the atmosphere. The carbonation of calcium‐based adsorbents using ambient conditions is particularly interesting for DAC due to its high theoretical CO2 uptake capacity and its low cost. In this paper, a new preparation method of synthetic calcium oxide‐based pellets for a DAC process was investigated. Their CO2 capture performance was studied experimentally in a fixed‐bed column and characterization was performed via Brunauer‐Emmett‐Teller (BET) analysis, mercury porosimetry, X‐ray diffraction, and scanning electron microscopy. Higher heating rates during the precursor calcination process and higher relative humidities during the carbonation process were found to lead to higher CO2 capture efficiencies. All prepared pellets showed good mechanical stability.

Analysis of the behaviour of limestone sorbents for sorption-enhanced gasification in dual interconnected fluidised bed reactor

Sorption-Enhanced Gasification (SEG) is a promising technology based on the use of Ca-based sorbents (like limestone) to selectively remove CO2 from the gasification environment, for production of hydrogen rich syngas. This process benefits from the extensive understanding of “calcium looping”, a post-combustion technique aimed at removing CO2 from flue gas. Calcium looping is most typically carried out in Dual Interconnected Fluidised Bed (DIFB) reactors. The correct design of sorbent looping processes in DIFB reactors must consider: 1) sorbent deactivation (i.e., decay of CO2 capture performance) over repeated cycling; 2) the loss of sorbent material due to elutriation, that may be enhanced by attrition and fragmentation. The aim of this study is to investigate six different commercial limestones in terms of sorbent performance and attrition/fragmentation tendency under simulated SEG conditions.The experimental campaign was carried out in a lab-scale DIFB reactor, electrically heated. The six sorbents were limestones coming from different parts of Europe. A synthetic gas including air, CO2 and N2 was used to simulate SEG conditions. A “test” consisted of ten complete cycles of calcination/carbonation. Calcination was performed at 850 °C, fluidising the bed with a stream of 10 % CO2 (balance air) to simulate oxidising conditions typical of the combustor-calciner. In the carbonation stage, the temperature was kept at 650 °C and the CO2 concentration was set at 10 % (balance nitrogen) to account for reducing conditions typical of the gasifier-carbonator.During each carbonation stage, the CO2 concentration at the exhaust was continuously monitored to calculate the CO2 specific capture performance. The sorbent attrition rate was determined by working out the mass of fines elutriated at the exhaust and collected in filters, for each calcination and carbonation stage. After a test, each exhaust sorbent sample was sieve-analysed to obtain the particle size distribution and the fraction of generated fragments. Moreover, the characterisation was extended by carrying out, in an ex situ apparatus, impact fragmentation tests on samples preprocessed in DIFB.Results were critically analysed in the light of the adopted operating conditions, by also including: (a) a fitting equation of conversion data, able to give indications on the sorbent resistance to sintering; (b) a carbonation reaction model, that allowed the estimation of the decrease in the sorbent specific surface area as long as the number of cycles increases.

CO2 capture based on Al2O3 ceramic membrane with hydrophobic modification

In this paper, Al2O3 ceramic membrane is modified to hydrophobicity by grafting 1 H,1 H,2 H,2 H-perfluorodecyltriethoxysilane. And its properties are characterized in detail. CO2 capture performance of ceramic membrane is investigated by experiments. Results show that wetting resistance after modification is significantly improved, and contact angle increases from the initial 49.8–130.9°. However, hydrophobic modification has no significant effect on the crystalline phase, surface morphology and pore size distribution of the ceramic membrane. With ethanolamine (MEA) as absorbent, CO2 mass transfer rate and capture efficiency using modified hydrophobic ceramic membrane are 46.6 × 10−3 mol/(m2·s) and 98.0%, showing significantly increase compared to the original membrane. After 72 h immersion in MEA solution, quality of ceramic membrane does not change significantly. And there is almost no change in average pore size. We believe this study will provide a reference for the industrial application for CO2 capture by gas-liquid membrane contactor with ceramic membrane.

High Temperature CO2 Capture Performance and Kinetic Analysis of Novel Potassium Stannate.

For the first time, the use of stannate-based sorbents was investigated as high temperature CO2 sorption to evaluate their potential to contribute towards reducing carbon emissions. The sorption capacity and kinetics of commercial tin oxide, sodium, potassium and calcium stannates and lab synthesised potassium stannates were tested using thermogravimetric analysis. Commercial K2SnO3 was found to possess the largest CO2 uptake capacity (2.77 mmol CO2/g or 12.2 wt%) at 700 °C, which is among the highest for potassium sorbents, but the CO2 desorption was not successful. On the contrary, the in-house synthesised K-stannate (K-B) using facile solid-state synthesis outperformed the other sorbents, resulting in a CO2 uptake of 7.3 wt% after 5 min, an adsorption rate (0.016 mg/s) one order of magnitude higher than the other stannates, and stability after 40 cycles. The XRD and XPS analyses showed that K-B contains a mixture of K2SnO3 (76%) and K4SnO4 (21%), while the Scherrer crystal sizes confirmed good resistance to sintering for the potassium stannates. Among the apparent kinetic model tested, the pseudo-second order model was the most suitable to predict the CO2 sorption process of K-B, indicating that chemical adsorption is dominant, while film-diffusion resistance and intra-particle diffusion resistance governed the sorption process in K-B. In summary, this work shows that solid-state synthesised potassium stannate could be an effective sorbent for high temperature separation, and additional work is required to further elucidate its potential.

Cigarette butt-assisted combustion synthesis of dolomite-derived sorbents with enhanced cyclic CO2 capturing capability for direct solar-driven calcium looping

Calcium looping (CaL) is a promising technology for CO2 capture owing to the widespread applicability and low-cost CaO-based sorbents. However, the SO2 and ash from coal combustion in O2/CO2 atmosphere for CaO regeneration is prone to cause rapid degradation for CaO-based sorbent. Hereby, a direct solar-driven CaL system is proposed to eliminate the adverse influence of coal combustion on CaO-based sorbent. Different unitary Mn-doped and binary-doped (Mn/Fe-, Mn/Cu- and Mn/Co-doped) dolomite-derived sorbents were synthesized by cigarette butt-assisted combustion method. The higher Mn doping ratio, the higher solar absorptance for unitary Mn-doped sorbent due to the gradually deepened blackness of the sample. Comprehensively considering the solar absorptance and CO2 capture performance, the unitary Mn-doped sorbent (Ca&Mg: Mn=100:10) is an optimal candidate, which has a solar absorptance of 63.6 % and a carbonation conversion of 64.3 % in the 20th cycle. Compared with the unitary Mn-doped sorbent (Ca&Mg: Mn=100:10), the binary-doped sorbent (Ca&Mg: Mn: Fe=100:5:5) exhibits a comparable CO2 capture capacity and a higher solar absorptance of 76.7 %. More importantly, the binary-doped sorbent (Ca&Mg: Mn: Fe=100:5:5) possesses the markedly faster CO2 capture rate in the early carbonation stage due to the increased lattice defect of CaO.

Potassium Silicate as Low-Temperature Binder in 3D-Printed Porous Structures for CO2 Separation.

Activated carbon sorbents were directly 3D-printed into highly adaptable monolithic/multi-channel systems by using potassium silicate as a low-temperature binder. By employing emerging 3D-printing technologies, monolithic structured sorbents were printed and fully characterized using N2, Ar, and CO2-sorption and Hg-intrusion porosimetry. The CO2-capture performance and the required temperature for active-site regeneration were evaluated by thermogravimetric analysis-looping experiments. A mechanically stable activated carbon sorbent was developed with an increased carbon capture performance, even when a room-temperature regeneration by N2 purging was applied. Although the CO2 uptake slightly dropped after several cycles due to incomplete recovery at room temperature, a capacity increase of 25% was observed in comparison with the original activated carbon powder. To improve the recovery of the active sorbent, an optimization of the desorption step was performed by increasing the regeneration temperature up to 150 °C. This resulted in a CO2 uptake of the composite material of 0.76 mmol/g, almost tripling the working capacity of the original activated carbon powder (0.28 mmol/g). An in situ X-ray diffraction study was carried out to confirm the proposed sorption mechanism, indicating the presence of potassium bicarbonates and confirming the combination of physisorption and chemisorption in our composites. Finally, the structured adsorbent was heated homogeneously by applying a current through the monolith. These results describe the development of a new type of 3D-printed regenerable CO2 sorbents by using potassium silicate as a low-temperature binder, providing high mechanical strength, good chemical and thermal stability, and improving the total CO2 capacity. Moreover, the developed monolith is showing a homogeneous resistivity, leading to uniform Joule heating of the CO2 adsorbent.

Design of hierarchically porous carbon frameworks for enhanced CO2 capture performance

To reduce the environmental impact of CO2, CO2 capture has become an area of research interest. Hierarchically porous materials have been certified as efficiency CO2 capture adsorbents. This work is aimed to construct hierarchically porous carbon frameworks (CPI-TPUs) with enhanced CO2 capture performance. CPI-TPUs are derived from polyimide (PI)/thermoplastic polyurethane (TPU) composite aerogels (PI-TPUs) with mesopores and macropores. Accordingly, the obtained CPI-TPU2 exhibits an improved CO2 uptake capacity (2.21 mmol/g, 298 K) compared to the pure CPI and PI-TPUs due to the synergistic effect of hierarchically pores, higher specific area and electron-rich heteroatoms. Specially, CPI-TPUs with pore volume ratio of mesopores/macropores to total pores in a range of 6–21 show high CO2 uptake performance. These CPI-TPUs with high CO2 adsorption capacities and suitable isosteric adsorption heats (Qst) are promising CO2 adsorbents.

CO2 capture and lipid production performance of microalgae in the S-shaped photobioreactor under different culture modes

An S-shaped photobioreactor was designed by adding grooves and baffles in the traditional photobioreactor to improve the culture efficiency of microalgae. After that, the parameters of the characterization of the S-shaped photobioreactor, such as the mixing time, gas holdup, and gas-liquid mass transfer coefficient, were determined. The biomass, lipid production rate, and average CO2 capture rate of microalgae were then analyzed under different culture modes. Finally, the feasibility of using digested piggery wastewater combined with simulated flue gas was explored as a culture mode for the microalgae and the lipid properties of the microalgae were analyzed. The results revealed that, at a flow rate of 0.08 vvm, the mixing time was reduced by 8.5 s, the gas hold-up increased by 44.6% and the gas–liquid mass transfer ability was also improved. Improvements were also observed in the biomass values, lipid production rate, and average CO2 capture rate of the microalgae under different culture conditions, with respective values reaching 0.23 g·(L·d)–1, 70.28 mg·(L·d)–1, and 0.43 g·(L·d)–1 under the mixotrophic mode. Additionally, digested piggery wastewater combined with the simulated microalgae flue gas culture was determined to be feasible. The biomass, lipid production rate, and the average CO2 capture rate of microalgae, the values of which were 0.22 g·(L·d)–1, 52.55 mg·(L·d)–1, and 0.41 g·(L·d)–1, respectively. Lipid was observed to have the potential to produce high-quality biofuel.

Enhanced CO2 Capture Durability and Mechanical Properties Using Cellulose-Templated CaO-Based Pellets with Steam Injection during Calcination

Cellulose-templated CaO-based pellets were prepared via an extrusion–spheronization method. However, the CO2 capture capacity of the modified sorbents still deteriorated rapidly after multiple cycles, and the mechanical properties were also reduced. Steam injection during calcination was conducted to enhance the CO2 capture performance of the sorbents. The modified pellets with 10 vol % steam injection present a faster carbonation rate compared to sorbents calcined under higher steam concentrations. A CO2 uptake of 0.32 g/g was obtained after 20 cycles, 133 and 60% higher than the raw sorbent and modified sorbent without steam reactivation. Moreover, the simultaneous thermal and atmosphere-induced sintering resulted in a nearly 4 times enhancement of the mechanical strength of the sorbents from 3.9 to 14.7 N. Under the harsh environment (calcined at 950 °C), the presence of steam further aggravated the sintering of the sorbent, resulting in a dramatic decrease in CO2 uptake.

Machine learning-driven assessment of relationship between activator properties in phase change solvent and its absorption performance for CO2 capture

Amine-based phase change solvents are recognized as an energy saving alternative to the benchmark solvent, mono-ethanolamine (MEA), for CO2 capture owing to their unique phase separation behavior and low energy penalty. However, screening of the phase change solvents is labor intensive via the experimental analysis. To address this issue, this work intends to develop a machine learning-driven assessment system to screen promising phase change solvents via exploring the relationship between activator properties and absorption performance. Based on the machine learning and quantum calculation, the relationships between 11 properties of 30 activators and 6 performance parameters were observed. Subsequently, the sensitive analysis was conducted via focusing on 5 key activator properties, such as alkalinity, hydrophobicity, molar refraction index, molar volume and the ADCH charge of N atom. Based on the proposed assessment system, 4 phase change solvents with potential excellent performance were screened, and kinetics and thermodynamics were further verified by experimental results. Among them, the regenerative heat of diethylenetriamine/N,N-Diethylethanolamine (DETA/DEEA) was around 2.44 GJ t−1, which is ∼ 34 % lower than that of benchmark MEA solvent. It is believed that the assessment system developed in this work can deepen the understanding of screening and practical application of phase change solvents.

Microscopic insight into the shaping of MOFs and its impact on CO2 capture performance.

The traditional synthesis method produces microcrystalline powdered MOFs, which prevents direct implementation in real-world applications which demand strict control of shape, morphology and physical properties. Therefore, shaping of MOFs via the use of binders is of paramount interest for their practical use in gas adsorption/separation, catalysis, sensors, etc. However, so far, the binders have been mostly selected by trial-and-error without anticipating the adhesion between the MOF and binder components to ensure the processability of homogeneous and mechanically stable shaped MOFs and the impact of the shaping on the intrinsic properties of the MOFs has been overlooked. Herein, we deliver a first systematic multiscale computational exploration of MOF/binder composites by selecting CALF-20, a prototypical MOF for real application in the field of CO2 capture, and a series of binders that cover a rather broad spectrum of properties in terms of rigidity/flexibility, porosity, and chemical functionality. The adhesion between the two components and hence the effectiveness of the shaping as well as the impact of the overall porosity of the CALF-20/binder on the CO2/N2 selectivity, CO2 sorption capacity and kinetics was analyzed. Shaping of CALF-20 by carboxymethyl cellulose was predicted to enable a fair compromise between excellent adhesion between the two components, whilst maintaining high CO2/N2 selectivity, large CO2 uptake and CO2 transport as fast as in the CALF-20. This multiscale computational tool paves the way towards the selection of an appropriate binder to achieve an optimum shaping of a given MOF in terms of processability whilst maintaining its high level of performance.

Capturing CO2 by ceria and ceria-zirconia nanomaterials of different origin.

Ceria and ceria-zirconia nanomaterials of different origin were studied in order to elucidate the role of their structural and textural characteristics in controlling the performance towards CO2 capture. Two commercial cerias and two home-prepared samples, CeO2 and CeO2-ZrO2 (75% CeO2) mixed oxide, were investigated. The samples were characterized by a number of analytical techniques including XRD, TEM, N2-adsorption, XPS, H2-TPR, Raman and FTIR spectroscopy. Static and dynamic CO2 adsorption experiments were applied to assess the CO2 capture performance. The type of surface species formed and their thermal stability were evaluated by in situ FTIR spectroscopy and CO2-TPD analysis. The two commercial ceria samples possessed similar structural and textural characteristics, formed the same types of carbonate-like surface species upon CO2 adsorption and, consequently, demonstrated almost identical CO2 capture performance under both static and dynamic conditions. The thermal stability of the adsorbed species increased in the order bidentate (B) carbonates, hydrogen carbonates (HC) and tridentate carbonates (T-III, T-II, T-I). Reduction of CeO2 increased the relative amount of the most strongly bonded T-I tridentate carbonates. Preadsorbed water led to hydroxylation and enhanced formation of hydrogen carbonates. Although the synthesized CeO2 sample had a higher surface area (by 30%) it showed a disadvantageous long mass transfer zone in the CO2-adsorption breakthrough curves. Because of its complex pore structure, this sample probably experiences severe intraparticle CO2 diffusion resistance. Having the same surface area as the synthesized CeO2, the mixed CeO2-ZrO2 oxide exhibited the highest CO2 capture capacity of 136 μmol g-1 under dynamic conditions. This was related to the highest concentration of CO2 adsorption sites (including defects) on this sample. The CeO2-ZrO2 system showed the lowest sensitivity to the presence of water vapor in the gas stream due to the lack of dissociative water adsorption on this material.