Data-driven design of metal-organic frameworks for wet flue gas CO2 capture.

Limiting the increase of CO2 in the atmosphere is one of the largest challenges of our generation1. Because carbon capture and storage is one of the few viable technologies that can mitigate current CO2 emissions2, much effort is focused on developing solid adsorbents that can efficiently capture CO2 from flue gases emitted from anthropogenic sources3. One class of materials that has attracted considerable interest in this context is metal-organic frameworks (MOFs), in which the careful combination of organic ligands with metal-ion nodes can, in principle, give rise to innumerable structurally and chemically distinct nanoporous MOFs. However, many MOFs that are optimized for the separation of CO2 from nitrogen4-7 do not perform well when using realistic flue gas that contains water, because water competes with CO2 for the same adsorption sites and thereby causes the materials to lose their selectivity. Although flue gases can be dried, this renders the capture process prohibitively expensive8,9. Here we show that data mining of a computational screening library of over 300,000 MOFs can identify different classes of strong CO2-binding sites-which we term 'adsorbaphores'-that endow MOFs with CO2/N2 selectivity that persists in wet flue gases. We subsequently synthesized two water-stable MOFs containing the most hydrophobic adsorbaphore, and found that their carbon-capture performance is not affected by water and outperforms that of some commercial materials. Testing the performance of these MOFs in an industrial setting and consideration of the full capture process-including the targeted CO2 sink, such as geological storage or serving as a carbon source for the chemical industry-will be necessary to identify the optimal separation material.

Core-shell nanostructured Cu-based bi-metallic electrocatalysts for co-production of ethylene and acetate.

Direct electrocatalytic CCU routes to produce a myriad of valuable chemicals (e.g., methanol, acetic acid, ethylene, propanol, among others) will allow the chemical industry to shift away from the conventional fossil-based production. Electrofuels need to go beyond the current electroreduction of CO2 to CO, and we will here demonstrate the continuous flow electroreduction of syngas (i.e., CO and H2), which are the products from CO2-to-CO, with enhanced product selectivity (∼90% towards ethylene). To overcome current drawbacks, including bicarbonate formation that resulted in low CO2 utilisation and low C2+ product selectivity, the development of nanostructured core-shell bi-metallic electrocatalysts for direct electrochemical reduction of syngas to C2+ is proposed. Electrosynthesis of ethylene is performed in a state-of-the-art continuous flow three-compartment cell to produce ethylene (cathodic gas phase product) and acetate (cathodic liquid phase product), simultaneously.

The Impact of Wettability on Dynamic Fluid Connectivity and Flow Transport Kinetics in Porous Media.

Usually, models describing flow and transport for sub-surface engineering processes at the Darcy-scale do not take into consideration the effects of pore-scale flow regimes and fluid connectivity on average flow functions. In this article, we investigate the impact of wettability on pore-scale flow regimes. We show that fluid connectivity at the pore scale has a significant impact on average flow kinetics and therefore its contribution should not be ignored. Immiscible two-phase flow simulations were performed in a two-dimensional model of a Berea sandstone rock for wettability conditions ranging from moderately water-wet to strongly oil-wet. The simulation results show that wettability has a strong impact on invading fluid phase connectivity, which subsequently influences flow transport resistance. The effect of invading-phase connectivity and ganglion dynamics (GD) on two-phase displacement kinetics was also investigated. It was found that invading phase connectivity decreases away from the neutrally wet (intermediate wet) state. This study provides evidence that GD accelerate fluid flow transport kinetics during immiscible displacement processes. Lastly, the impact of wettability on fluid displacement efficiency and residual saturations was investigated. Maximum displacement efficiency occurred at the neutrally wet state.

Manufacturing of Microfluidic Devices with Interchangeable Commercial Fiber Optic Sensors.

In situ measurements are highly desirable in many microfluidic applications because they enable real-time, local monitoring of physical and chemical parameters, providing valuable insight into microscopic events and processes that occur in microfluidic devices. Unfortunately, the manufacturing of microfluidic devices with integrated sensors can be time-consuming, expensive, and "know-how" demanding. In this article, we describe an easy-to-implement method developed to integrate various "off-the-shelf" fiber optic sensors within microfluidic devices. To demonstrate this, we used commercial pH and pressure sensors ("pH SensorPlugs" and "FOP-MIV", respectively), which were "reversibly" attached to a glass microfluidic device using custom 3D-printed connectors. The microfluidic device, which serves here as a demonstrator, incorporates a uniform porous structure and was manufactured using a picosecond pulsed laser. The sensors were attached to the inlet and outlet channels of the microfluidic pattern to perform simple experiments, the aim of which was to evaluate the performance of both the connectors and the sensors in a practical microfluidic environment. The bespoke connectors ensured robust and watertight connection, allowing the sensors to be safely disconnected if necessary, without damaging the microfluidic device. The pH SensorPlugs were tested with a pH 7.01 buffer solution. They measured the correct pH values with an accuracy of ±0.05 pH once sufficient contact between the injected fluid and the measuring element (optode) was established. In turn, the FOP-MIV sensors were used to measure local pressure in the inlet and outlet channels during injection and the steady flow of deionized water at different rates. These sensors were calibrated up to 140 mbar and provided pressure measurements with an uncertainty that was less than ±1.5 mbar. Readouts at a rate of 4 Hz allowed us to observe dynamic pressure changes in the device during the displacement of air by water. In the case of steady flow of water, the pressure difference between the two measuring points increased linearly with increasing flow rate, complying with Darcy's law for incompressible fluids. These data can be used to determine the permeability of the porous structure within the device.

Review of Microfluidic Devices and Imaging Techniques for Fluid Flow Study in Porous Geomaterials.

Understanding transport phenomena and governing mechanisms of different physical and chemical processes in porous media has been a critical research area for decades. Correlating fluid flow behaviour at the micro-scale with macro-scale parameters, such as relative permeability and capillary pressure, is key to understanding the processes governing subsurface systems, and this in turn allows us to improve the accuracy of modelling and simulations of transport phenomena at a large scale. Over the last two decades, there have been significant developments in our understanding of pore-scale processes and modelling of complex underground systems. Microfluidic devices (micromodels) and imaging techniques, as facilitators to link experimental observations to simulation, have greatly contributed to these achievements. Although several reviews exist covering separately advances in one of these two areas, we present here a detailed review integrating recent advances and applications in both micromodels and imaging techniques. This includes a comprehensive analysis of critical aspects of fabrication techniques of micromodels, and the most recent advances such as embedding fibre optic sensors in micromodels for research applications. To complete the analysis of visualization techniques, we have thoroughly reviewed the most applicable imaging techniques in the area of geoscience and geo-energy. Moreover, the integration of microfluidic devices and imaging techniques was highlighted as appropriate. In this review, we focus particularly on four prominent yet very wide application areas, namely "fluid flow in porous media", "flow in heterogeneous rocks and fractures", "reactive transport, solute and colloid transport", and finally "porous media characterization". In summary, this review provides an in-depth analysis of micromodels and imaging techniques that can help to guide future research in the in-situ visualization of fluid flow in porous media.

Photo-generation of cyclic carbonates using hyper-branched Ru-TiO2.

Anthropogenic CO2 is the main contributor to the increased concentration of greenhouse gases in the atmosphere, and thus utilising waste CO2 for the production of valuable chemicals is a very appealing strategy for reducing CO2 emissions. The catalytic fixation of CO2 with epoxides for the production of cyclic carbonates has gained increasing attention from the research community in search of an alternative to the homogeneous catalytic routes, which are currently being used in industry. A novel photocatalytic heterogeneous approach to generate cyclic carbonates is demonstrated in this work. Hyper-branched microstructured Ru modified TiO2 nanorods decorated with RuO2 nanoparticles, supported on fluorine-doped tin oxide (FTO) glass were fabricated for the first time and were used to catalyse the photo-generation of propylene carbonates from propylene oxides. Propylene carbonate was used as a reference for cyclic carbonates. The photo-generation of cyclic carbonates from epoxides and CO2 was carried out at a maximum temperature of 55 °C at 200 kPa in a stainless steel photoreactor with a quartz window, under solar irradiation for 6 h. The best performing photocatalyst exhibited an estimated selectivity of 83% towards propylene carbonates under the irradiation of a solar simulator.

A microfluidic photoelectrochemical cell for solar-driven CO2 conversion into liquid fuels with CuO-based photocathodes.

Utilising photoelectrochemical (PEC) devices to produce sustainable fuels from water and CO2 is a very attractive strategy, in which sunlight is used to convert the greenhouse gas (CO2) into a usable form of stored chemical energy. While significant progress has been made in the development of efficient photoactive catalysts for PEC reactions, limited efforts have been focused on the reactor design where continuous flow microfluidic PEC reactors are particular promising. In this work, a range of CuO-based thin films were used as photocathodes in a continuous flow microfluidic PEC reactor using CO2-saturated aqueous NaHCO3 solution under simulated AM 1.5 solar irradiation for up to 12 h. The highest photocurrent density obtained was for the α-Fe2O3/CuO photoelectrode yielding -1.0 mA cm-2 at 0.3 V vs. RHE and initial results indicated a solar-to-fuel (STF) efficiency of 0.48%. While the CuO, Cu2O and CuO-Cu2O photoelectrodes virtually only formed formate, the bilayer α-Fe2O3/CuO photocathode produced methanol in addition to formate indicating that combined copper and iron oxides in continuous flow microfluidic PEC cells have great potential of direct solar conversion into useful chemicals.

Carbon dioxide sequestration using NaHSO4 and NaOH: A dissolution and carbonation optimisation study.

The use of NaHSO4 to leach out Mg fromlizardite-rich serpentinite (in form of MgSO4) and the carbonation of CO2 (captured in form of Na2CO3 using NaOH) to form MgCO3 and Na2SO4 was investigated. Unlike ammonium sulphate, sodium sulphate can be separated via precipitation during the recycling step avoiding energy intensive evaporation process required in NH4-based processes. To determine the effectiveness of the NaHSO4/NaOH process when applied to lizardite, the optimisation of the dissolution and carbonation steps were performed using a UK lizardite-rich serpentine. Temperature, solid/liquid ratio, particle size, concentration and molar ratio were evaluated. An optimal dissolution efficiency of 69.6% was achieved over 3 h at 100 °C using 1.4 M sodium bisulphate and 50 g/l serpentine with particle size 75-150 µm. An optimal carbonation efficiency of 95.4% was achieved over 30 min at 90 °C and 1:1 magnesium:sodium carbonate molar ratio using non-synthesised solution. The CO2 sequestration capacity was 223.6 g carbon dioxide/kg serpentine (66.4% in terms of Mg bonded to hydromagnesite), which is comparable with those obtained using ammonium based processes. Therefore, lizardite-rich serpentinites represent a valuable resource for the NaHSO4/NaOH based pH swing mineralisation process.

In-situ multicore fibre-based pH mapping through obstacles in integrated microfluidic devices.

Microfluidic systems with integrated sensors are ideal platforms to study and emulate processes such as complex multiphase flow and reactive transport in porous media, numerical modeling of bulk systems in medicine, and in engineering. Existing commercial optical fibre sensing systems used in integrated microfluidic devices are based on single-core fibres, limiting the spatial resolution in parameter measurements in such application scenarios. Here, we propose a multicore fibre-based pH system for in-situ pH mapping with tens of micrometer spatial resolution in microfluidic devices. The demonstration uses custom laser-manufactured glass microfluidic devices (called further micromodels) consisting of two round ports. The micromodels comprise two lintels for the injection of various pH buffers and an outlet. The two-port system facilitates the injection of various pH solutions using independent pressure pumps. The multicore fibre imaging system provides spatial information about the pH environment from the intensity distribution of fluorescence emission from the sensor attached to the fibre end facet, making use of the cores in the fibre as independent measurement channels. As proof-of-concept, we performed pH measurements in micromodels through obstacles (glass and rock beads), showing that the particle features can be clearly distinguishable from the intensity distribution from the fibre sensor.

Facile Synthesis of Gram-Scale Mesoporous Ag/TiO2 Photocatalysts for Pharmaceutical Water Pollutant Removal and Green Hydrogen Generation.

This work demonstrates a two-step gram-scale synthesis of presynthesized silver (Ag) nanoparticles impregnated with mesoporous TiO2 and evaluates their feasibility for wastewater treatment and hydrogen gas generation under natural sunlight. Paracetamol was chosen as the model pharmaceutical pollutant for evaluating photocatalytic performance. A systematic material analysis (morphology, chemical environment, optical bandgap energy) of the Ag/TiO2 photocatalyst powder was carried out, and the influence of material properties on the performance is discussed in detail. The experimental results showed that the decoration of anatase TiO2 nanoparticles (size between 80 and 100 nm) with 5 nm Ag nanoparticles (1 wt %) induced visible-light absorption and enhanced charge carrier separation. As a result, 0.01 g/L Ag/TiO2 effectively removed 99% of 0.01 g/L paracetamol in 120 min and exhibited 60% higher photocatalytic removal than pristine TiO2. Alongside paracetamol degradation, Ag/TiO2 led to the generation of 1729 µmol H2 g-1 h-1. This proof-of-concept approach for tandem pollutant degradation and hydrogen generation was further evaluated with rare earth metal (lanthanum)- and nonmetal (nitrogen)-doped TiO2, which also showed a positive response. Using a combination of ab initio calculations and our new theory model, we revealed that the enhanced photocatalytic performance of Ag/TiO2 was due to the surface Fermi-level change of TiO2 and lowered surface reaction energy barrier for water pollutant oxidation. This work opens new opportunities for exploiting tandem photocatalytic routes beyond water splitting and understanding the simultaneous reactions in metal-doped metal oxide photocatalyst systems under natural sunlight.

Photoelectrocatalytic Surfactant Pollutant Degradation and Simultaneous Green Hydrogen Generation.

For the first time, we demonstrate a photoelectrocatalysis technique for simultaneous surfactant pollutant degradation and green hydrogen generation using mesoporous WO3/BiVO4 photoanode under simulated sunlight irradiation. The materials properties such as morphology, crystallite structure, chemical environment, optical absorbance, and bandgap energy of the WO3/BiVO4 films are examined and discussed. We have tested the anionic type (sodium 2-naphthalenesulfonate (S2NS)) and cationic type surfactants (benzyl alkyl dimethylammonium compounds (BAC-C12)) as model pollutants. A complete removal of S2NS and BAC-C12 surfactants at 60 and 90 min, respectively, by applying 1.75 V applied potential vs RHE to the circuit, under 1 sun was achieved. An interesting competitive phenomenon for photohole utilization was observed between surfactants and adsorbed water. This led to the formation of H2O2 from water alongside surfactant degradation (anode) and hydrogen evolution (cathode). No byproducts were observed after the direct photohole mediated degradation of surfactants, implying its advantage over other AOPs and biological processes. In the cathode compartment, 82.51 µmol/cm2 and 71.81 µmol/cm2 of hydrogen gas were generated during the BAC-C12 and S2NS surfactant degradation process, respectively, at 1.75 V RHE applied potential.

Highly selective CO2 photoreduction to CO on MOF-derived TiO2.

Metal-Organic Framework (MOF)-derived TiO2, synthesised through the calcination of MIL-125-NH2, is investigated for its potential as a CO2 photoreduction catalyst. The effect of the reaction parameters: irradiance, temperature and partial pressure of water was investigated. Using a two-level design of experiments, we were able to evaluate the influence of each parameter and their potential interactions on the reaction products, specifically the production of CO and CH4. It was found that, for the explored range, the only statistically significant parameter is temperature, with an increase in temperature being correlated to enhanced production of both CO and CH4. Over the range of experimental settings explored, the MOF-derived TiO2 displays high selectivity towards CO (98%), with only a small amount of CH4 (2%) being produced. This is notable when compared to other state-of-the-art TiO2 based CO2 photoreduction catalysts, which often showcase lower selectivity. The MOF-derived TiO2 was found to have a peak production rate of 8.9 × 10-4 µmol cm-2 h-1 (2.6 µmol g-1 h-1) and 2.6 × 10-5 µmol cm-2 h-1 (0.10 µmol g-1 h-1) for CO and CH4, respectively. A comparison is made to commercial TiO2, P25 (Degussa), which was shown to have a similar activity towards CO production, 3.4 × 10-3 µmol cm-2 h-1 (5.9 µmol g-1 h-1), but a lower selectivity preference for CO (3 : 1 CH4 : CO) than the MOF-derived TiO2 material developed here. This paper showcases the potential for MIL-125-NH2 derived TiO2 to be further developed as a highly selective CO2 photoreduction catalyst for CO production.

Investigation of CO2 Photoreduction in an Annular Fluidized Bed Photoreactor by MP-PIC Simulation.

Carbon dioxide (CO2) photoreduction is a promising process for both mitigating CO2 emissions and providing chemicals and fuels. A gas-solid two-phase annular fluidized bed photoreactor (FBPR) would be preferred for this process due to its high mass-transfer rate and easy operation. However, CO2 photoreduction using the FBPR has not been widely researched to date. The Lagrangian multiphase particle-in-cell (MP-PIC) simulation with computational fluid dynamic models is a new and robust approach to explore the multiphase reaction system in the gas-solid fluidized bed. Therefore, the purpose of this paper is to investigate CO2 photoreduction in the FBPR by MP-PIC modeling to understand the intrinsic mechanism of solid flow, species mass transfer, and CO2 photoreaction. The MP-PIC models for solid flow in the FBPR were validated by the bed expansion height and bubble size. The results showed the particle stress of the Lun model, the drag of the Ergun-WenYu (Gidaspow) model, and the coefficient of restitution e = 0.95 with the wall parameters e w = 0.9 and µw = 0.6 are the best fit to the experimental empirical correlations. The MP-PIC models developed in this work proved to be better than the Eulerian two-fluid modeling in the prediction of the bed expansion height and bubble size. It was also found from the simulation results that the maximum radiation intensity is in the half reactor height area, and the photocatalytic reaction mainly occurred around the inner wall. It showed that the gas velocity and catalyst loading were two crucial operating parameters to control the process. The results reported here can provide guidance for the operation and reactor design of the CO2 photoreduction process.

Core-shell TiO2-x-CuyO microspheres for photogeneration of cyclic carbonates under simulated sunlight.

Propylene carbonates are important organic solvents and feedstocks for different applications, including synthesis of polymers and Li-batteries. The generation of propylene carbonate utilising anthropogenic CO2 and renewable solar energy offers an alternative sustainable process with a closed loop carbon cycle. The development of microstructured photocatalysts with desired properties, including high degree of product selectivity, wide range of optical properties, and maximised conversion yield, plays an important role for effective production of propylene carbonate from CO2. A hierachical hollow core with a double shell of TiO2-x-Cu2O-CuO was fabricated using the versatile solvothermal-microwave synthesis method. The fabricated sample revealed effective cascading of photogenerated electrons and holes that promoted the conversion of propylene carbonate (i.e., 1.6 wt%) under 1 Sun irradiation.

Understanding the role of wettability distribution on pore-filling and displacement patterns in a homogeneous structure via quasi 3D pore-scale modelling.

Most numerical simulation studies have focused on the effect of homogenous wettability on fluid flow dynamics; however, most rocks display spatially heterogeneous wettability. Therefore, we have used direct numerical simulations (DNS) to investigate wettability heterogeneity at pore-scale. We have built a quasi-3D pore-scale model and simulated two-phase flow in a homogenous porous media with homogenous and heterogeneous wettability distributions. Five different heterogeneous wettability patterns were used in this study. We observed that heterogenous wettability significantly affects the evolution of fluid interface, trapped saturation, and displacement patterns. Wettability heterogeneity results in fingering and specific trapping patterns which do not follow the flow behaviour characteristic of a porous medium with homogenous wettability. This flow behaviour indicates a different flow regime that cannot be estimated using homogenous wettability distributions represented by an average contact angle. Moreover, our simulation results show that certain spatial configurations of wettability heterogeneity at the microscale, e.g. being perpendicular to the flow direction, may assist the stability of the displacement and delay the breakthrough time. In contrast, other configurations such as being parallel to the flow direction promote flow instability for the same pore-scale geometry.

Acetate intercalated Mg-Al layered double hydroxides (LDHs) through modified amide hydrolysis: a new route to synthesize novel mixed metal oxides (MMOs) for CO2 capture.

Layered double hydroxide (LDH) based mixed metal oxides (MMOs) are promising high temperature CO2 capture sorbents. In order to improve their CO2 capture capacity, it is crucial to bring in changes to their physicochemical properties such as morphology, particle size, surface area and activity by tuning the synthesis method. Here we report a modified amide hydrolysis method to synthesize LDHs with a mixed morphology and better CO2 capture properties. Acetate intercalated Mg-Al LDHs with two different Mg/Al ratios (3 and 4) were synthesized by employing metal hydroxides as the starting precursors and acetamide as the hydrolysing agent. The resultant LDHs crystallized in a new morphology having a combination of both fibrous and sheet like crystallites. The MMOs derived from Mg-Al-acetate LDHs retained the mixed morphology observed in the precursor LDHs. The resultant MMOs showed almost a threefold increase in the BET surface area, 316 (Mg/Al = 3) and 341 (Mg/Al = 4) m2 g-1, compared to MMOs derived from anion exchanged Mg-Al-acetate LDH (118 m2 g-1). The MMOs synthesized by acetamide hydrolysis captured 1.2 mmol g-1 and 0. 87 mmol g-1 of CO2 at 200 and 300 °C (atmospheric pressure), respectively. The CO2 capture capacity realized was increased more than twofold compared to the CO2 capture capacity of MMOs derived from anion exchanged acetate LDH (0.57 mmol g-1) tested under similar conditions. The developed MMOs showed promising CO2 capture (1.0 mmol g-1) capacity at industrially relevant CO2 concentration (14%).

Hierarchical hyper-branched titania nanorods with tuneable selectivity for CO2 photoreduction.

Utilising captured CO2 and converting it into solar fuels can be extremely beneficial in reducing the constantly rising CO2 concentration in the atmosphere while simultaneously addressing energy crisis issues. Hence, many researchers have focused their work on the CO2 photoreduction reaction for the last 4 decades. Herein, the titania hyper-branched nanorod (HBN) thin films, with a novel hierarchical dendritic morphology, revealed enhanced CO2 photoreduction performance. The HBNs exhibited enhanced photogenerated charge production (66%), in comparison with P25 (39%), due to the unique hyper-branched morphology. Furthermore, the proposed HBN thin films exhibited a high degree of control over the product selectivity, by undergoing a facile phase-altering treatment. The selectivity was shifted from 91% towards CO, to 67% towards CH4. Additionally, the HBN samples showed the potential to surpass the conversion rates of the benchmark P25 TiO2 in both CO and CH4 production. To further enhance the selectivity and overall performance of the HBNs, RuO2 was incorporated into the synthesis, which enhanced the CH4 selectivity from 67% to 74%; whereas the incorporation of CuO revealed a selectivity profile comparative to P25.

Layered Double Hydroxides-Based Mixed Metal Oxides: Development of Novel Structured Sorbents for CO2 Capture Applications.

Layered double hydroxide (LDHs)-based mixed metal oxides (MMOs) are widely studied as the medium to high temperature (200-400 °C) CO2 capture sorbents. However, most of the studies are carried out using the powdered samples. To upgrade these sorbents for industrial-scale CO2 capture, it is important to move away from the powdered form and develop structured sorbents. Moreover, the CO2 capture properties of these sorbents need to be improved in terms of capture capacity and cycling stability. Here we are utilizing a modified amide hydrolysis method to improve the CO2 capture capacities of LDHs-based MMOs. Subsequently, aqueous exfoliation coupled with the freeze-drying technique was utilized to develop LDHs-based novel MMOs. Exfoliated LDH nano sheets were pelletized (2 mm) to circumvent the challenges associated with powder samples when used in industrial-scale applications. The obtained pellets have an average crushing load of 11.1 N and 4.3 MPa of compressive strength, which indicate their good mechanical stability. The MMOs pellets showed a narrow distribution of pores (8-10 nm) with very good surface area (264 m2/g) and pore volume (1.27 cm3/g). They also had much improved CO2 capture capacities at ambient pressure and both low (2.17 mmol/g, 30 °C) and medium temperature (1.43 mmol/g, 200 °C), as compared to previously reported pristine MMOs powder samples. The pelletized structured sorbents also outperformed commercial LDH-based pellets by several fold.

The effect of the layer-interlayer chemistry of LDHs on developing high temperature carbon capture materials.

The layer-interlayer chemistry of layered double hydroxides (LDHs) offers a vast opportunity to develop mixed metal oxides (MMOs) as novel sorbents for high temperature CO2 capture. Here, we report the synthesis of adamantanecarboxylate intercalated Ca-Al LDH by employing a co-hydration method. Thermal decomposition under a controlled atmosphere converts the layered metal hydroxides to MMOs and an intercalated anion into a carbonaceous support. The higher thermal stability and polymeric nature of the intercalated adamantanecarboxylate ion act as a thermal/mechanical support for the layered MMOs. The resultant hybrid solid sorbent shows excellent high temperature CO2 capture and cycling performance under both CO2 rich and lean (industrial flue gas) conditions. The hybrid sample shows almost 100% carbonation of all the active phase present, leading to maximum atom efficiency. The hybrid sorbent also shows rapid kinetics for both the carbonation and regeneration steps. The employed synthetic strategy offers a new approach to develop improved novel sorbents based on LDHs for high temperature CO2 capture.

Advanced High-Temperature CO2 Sorbents with Improved Long-Term Cycling Stability.

Developing novel sorbents with maximum carbonation efficiency and good cycling stability for CO2 capture is a promising route to sequester anthropogenic CO2. In this work, we have employed a green synthesis method to synthesize CaO-based sorbents suitably stabilized by MgO and supported by in situ generated carbon under inert atmosphere. The varied amounts (10-30 wt %) of MgO were used to stabilize the CaO. The supported mixed metal oxide (MMO) sorbents were screened for high-temperature CO2 capture under CO2 rich (86% CO2) and lean (14% CO2) gas streams at 650 °C and atmospheric pressure. The MMO sorbents captured 53-63 wt % of CO2 per gram of sorbent under 86 and 14% CO2, accounting for about 98% carbonation efficiency, which outperforms the CO2 capture capacity of limestone derived CaO (L-CaO) sorbents (22.8 wt %). All of the synthetic MMO sorbents showed greater capture capacity and cyclic stability when compared to benchmark L-CaO. Because of the high carbonation efficiency and cycling stability of g-Ca0.69Mg0.3O sorbent, it was tested for 100 carbonation/regeneration cycles of 5 min each under CO2 lean conditions. The g-Ca0.69Mg0.3O sorbent showed exceptional CO2 capture capacity and cycling stability and retained about 65% of its initial capture capacity after 100 cycles.