Optimization of the structural characteristics of CaO and its effective stabilization yield high-capacity CO2 sorbents

3D Ordered Macroporous Mn, Zr-Doped CaCO3 Nanomaterials for Stable Thermochemical Energy Storage

Developing high-performance Ca-based materials that can work for long-term heat transfer and storage in concentrated solar power plants is crucial to achieve the large-scale conversion of solar photon fluxes to dispatchable electricity. This work demonstrates that a series of Mn, Zr co-doped CaCO3 nanomaterials with the 3D ordered macroporous (3DOM) skeletons are successfully prepared by a novel strategy of templated metal salt co-precipitation. The characterization results indicate that a majority of Zr and Mn are atomically dispersed into the highly-crystallized CaCO3 framework, whereas a minor amount of Mn is present in the form of CaMnO3 nanoparticles (NPs). The optimal 3DOM material made by templating with PS microspheres with a diameter of ≈350 nm, 3DOM-Ca80Mn10Zr10, shows a solar light absorptance of ≈74.1% and an initial energy storage density of 1706.4 kJ kg-1. Importantly, it gives an impressive energy storage density loss of < 6.0% and maintains above 1600 kJ kg-1 after 125 cycles. The density functional theory calculations reveal that the co-doping of Mn and Zr into the CaO crystal lattice offers a strong affinity to [Ca4O4] clusters, as a result, the anti-sintering of CaO NPs is significantly enhanced under high temperature.

Ionic Diffusion in CO_{2} Adsorption by Li_{4}SiO_{4}: Inert-Marker Experiment and DFT Calculations

CO_{2} adsorption by Li_{4}SiO_{4} has garnered significant attention for its potential in effectively capturing CO_{2}. The slow diffusion-controlled reaction within the product layer is a key factor affecting CO_{2} adsorption. However, no research has been conducted to study the diffusion mechanism. Here, ionic diffusion was systematically comprehended through inert-marker experiments and first-principles calculations. An electron probe test clearly captures the movement of inert-marker Pt into the product layer, thus the outward transfer of O^{2-} and Li^{+} ions is proposed to be the dominant diffusion mode. Density functional theory calculations also confirm the diffusion of O^{2-} and Li^{+} with the former being the speed controlling step.

An alumina phase induced composite transition shuttle to stabilize carbon capture cycles

Limiting global warming to 1.5-2 °C requires a 50-90% reduction in CO2 emissions in 2050, depending on different scenarios, and carbon capture, utilization, and storage is a promising technology that can help reach this objective. Calcium oxide (CaO) carbon capture is an appealing choice because of its affordability, large potential capacity, and ability to withstand the high temperatures of flue gases. However, the structural instability and capacity fading challenge its large-scale industrial applications. Here, we design a reversible reaction shuttle in CaO-based sorbents to improve the structure stability by changing the initial alumina phases. Diverse alumina phases (x-Al2O3) are first synthesized and utilized as the aluminum source for creating CaO@x-Al2O3 composites. As expected, the CaO@δ-Al2O3 composite demonstrates a carbon capture capacity of 0.43 g-CO2/g-sorbent after 50 cycles, with an impressive capacity retention of 82.7%. Combined characterizations and calculations reveal that this stability improvement is attributed to a transition shuttle between Ca3Al2O6 and Ca5Al6O14, which can effectively restrain the complete decompositions of those structure-stabilized intermediate phases. An economic assessment further identifies the significance of heat transfer efficiency improvement upon cycles, and control of capital/operation cost, energy price and carbon tax for a future cost-effective commercialization of current strategy.

Ca-based materials derived from calcined cigarette butts for CO2 capture and thermochemical energy storage

Cigarette butts (CBs) are one of the most common types of litter in the world. Due to the toxic substances they contain, the waste generated poses a harmful risk to the environment, and therefore there is an urgent need for alternative solutions to landfill storage. Thus, this work presents a possible revalorization of this waste material, which implies interesting environmental benefits. CBs were used as sacrificial templates for the preparation of CaO-based materials by impregnation with calcium and magnesium nitrates followed by flaming combustion. These materials presented enhanced porosity for their use in the Calcium Looping process applied either to thermochemical energy storage or CO2 capture applications. The influence of the concentration of Ca and Mg in the impregnating solutions on the multicycle reactivity of the samples was studied. An improved multicycle performance was obtained in terms of conversion for both applications.

Dual Functional Materials: At the Interface of Catalysis and Separations

Dual functional materials (DFMs) are a promising approach to increase the energy efficiency of carbon capture and utilization by combining both steps into a single unit operation. In this Perspective, we analyze the challenges and opportunities of integrated carbon capture and utilization (ICCU) via a thermally driven process. We identify three key areas that will facilitate research progress toward industrially viable solutions: (1) selecting appropriate DFM operating conditions; (2) designing and characterizing interfacial site cooperativity for CO2 adsorption and hydrogenation; and (3) establishing standards for rigorous and comprehensive data reporting.

Review on the modifications of natural and industrial waste CaO based sorbent of calcium looping with enhanced CO2 capture capacity

The calcium looping cycle (CaL) possesses outstanding CO2 capture capacity for future carbon-capturing technologies that utilise CaO sorbents to capture the CO2 in a looping cycle. However, sorbent degradation and the presence of inert materials stabilise the sorbent, thereby reducing the CO2 capture capacity. Consequently, the CaO sorbent that has degraded must be replenished, increasing the operational cost for industrial use. CaO sorbents have been modified to enhance their CO2 capture capacity and stability. However, various CaO sorbents, including limestone, dolomite, biogenesis calcium waste and industrial waste, exhibit distinct behaviour in response to these modifications. Thus, this work comprehensively reviews the CO2 capture capacity of sorbent improvement based on various CaO sorbents. Furthermore, this study provides an understanding of the effects of CO2 capture capacity based on the properties of the CaO sorbent. The properties of various CaO sorbents, such as surface area, pore volume, particle size and morphology, are influential in exhibiting high CO2 capture capacity. This review provides insights into the future development of CaL technology, particularly for carbon-capturing technologies that focus on the modifications of CaO sorbents and the properties that affect the CO2 capture capacity.

Synthesis of core@shell catalysts guided by Tammann temperature

Designing high-performance thermal catalysts with stable catalytic sites is an important challenge. Conventional wisdom holds that strong metal-support interactions can benefit the catalyst performance, but there is a knowledge gap in generalizing this effect across different metals. Here, we have successfully developed a generalizable strong metal-support interaction strategy guided by Tammann temperatures of materials, enabling functional oxide encapsulation of transition metal nanocatalysts. As an illustrative example, Co@BaAl2O4 core@shell is synthesized and tracked in real-time through in-situ microscopy and spectroscopy, revealing an unconventional strong metal-support interaction encapsulation mechanism. Notably, Co@BaAl2O4 exhibits exceptional activity relative to previously reported core@shell catalysts, displaying excellent long-term stability during high-temperature chemical reactions and overcoming the durability and reusability limitations of conventional supported catalysts. This pioneering design and widely applicable approach has been validated to guide the encapsulation of various transition metal nanoparticles for environmental tolerance functionalities, offering great potential to advance energy, catalysis, and environmental fields.

Solution combustion synthesis of MgO-stabilized CaO sorbents using polyethylene glycol as fuel and dispersant

The main limit for the calcium looping process is the sharp decrease of the capture capacity of the CO2 sorbents during multiple cycles. In this research, a solution combustion method was employed to synthesize MgO-stabilized CaO sorbents. Polyethylene glycol (PEG) was used as the fuel and dispersant, with the purpose to enhance the uniformity of the Ca and Mg distributions in the sorbent. The results show that highly reactive MgO-stabilized CaO sorbents can be obtained through a solution combustion method using PEG as the fuel and dispersant. The existence of MgO can effectively restrain the sintering of the sorbent, resulting in a more porous and stable micro-structure of the sorbent. The CO2 capture capacity of the MgO-stabilized CaO sorbent synthesized under the optimum conditions is 0.40 g(CO2)/g(sorbent) after 20 cycles, which is 75.3% higher than CaCO3.

Of Glasses and Crystals: Mitigating the Deactivation of CaO-Based CO2 Sorbents through Calcium Aluminosilicates

CaO-based sorbents are cost-efficient materials for high-temperature CO2 capture, yet they rapidly deactivate over carbonation-regeneration cycles due to sintering, hindering their utilization at the industrial scale. Morphological stabilizers such as Al2O3 or SiO2 (e.g., introduced via impregnation) can improve sintering resistance, but the sorbents still deactivate through the formation of mixed oxide phases and phase segregation, rendering the stabilization inefficient. Here, we introduce a strategy to mitigate these deactivation mechanisms by applying (Al,Si)Ox overcoats via atomic layer deposition onto CaCO3 nanoparticles and benchmark the CO2 uptake of the resulting sorbent after 10 carbonation-regeneration cycles against sorbents with optimized overcoats of only alumina/silica (+25%) and unstabilized CaCO3 nanoparticles (+55%). 27Al and 29Si NMR studies reveal that the improved CO2 uptake and structural stability of sorbents with (Al,Si)Ox overcoats is linked to the formation of glassy calcium aluminosilicate phases (Ca,Al,Si)Ox that prevent sintering and phase segregation, probably due to a slower self-diffusion of cations in the glassy phases, reducing in turn the formation of CO2 capture-inactive Ca-containing mixed oxides. This strategy provides a roadmap for the design of more efficient CaO-based sorbents using glassy stabilizers.

Constructing Hollow Multishelled Microreactors with a Nanoconfined Microenvironment for Ofloxacin Degradation through Peroxymonosulfate Activation: Evolution of High-Valence Cobalt-Oxo Species

This study constructed hollow multishelled microreactors with a nanoconfined microenvironment for degrading ofloxacin (OFX) through peroxymonosulfate (PMS) activation in Fenton-like advanced oxidation processes (AOPs), resulting in adequate contaminant mineralization. Among the microreactors, a triple-shelled Co-based hollow microsphere (TS-Co/HM) exhibited optimal performance; its OFX degradation rate was 0.598 min-1, which was higher than that of Co3O4 nanoparticles by 8.97-fold. The structural tuning of Co/HM promoted the formation of oxygen vacancies (VO), which then facilitated the evolution of high-valence cobalt-oxo (Co(IV)═O) and shifted the entire t2g orbital of the Co atom upward, promoting catalytic reactions. Co(IV)═O was identified using a phenylmethyl sulfoxide (PMSO) probe and in situ Raman spectroscopy, and theoretical calculations were conducted to identify the lower energy barrier for Co(IV)═O formation on the defect-rich catalyst. Furthermore, the TS-Co/HM catalyst exhibited remarkable stability in inorganic (Cl-, H2PO4-, and NO3-), organic (humic acid), real water samples (tap water, river water, and hospital water), and in a continuous flow system in a microreactor. The nanoconfined microenvironment could enrich reactants in the catalyst cavities, prolong the residence time of molecules, and increase the utilization efficiency of Co(IV)═O. This work describes an activation process involving Co(IV)═O for organic contaminants elimination. Our results may encourage the use of multishelled structures and inform the design of nanoconfined catalysts in AOPs.

Synergistic promotions between CO2 capture and in-situ conversion on Ni-CaO composite catalyst

The integrated CO₂ capture and conversion (iCCC) technology has been booming as a promising cost-effective approach for Carbon Neutrality. However, the lack of the long-sought molecular consensus about the synergistic effect between the adsorption and in-situ catalytic reaction hinders its development. Herein, we illustrate the synergistic promotions between CO₂ capture and in-situ conversion through constructing the consecutive high-temperature Calcium-looping and dry reforming of methane processes. With systematic experimental measurements and density functional theory calculations, we reveal that the pathways of the reduction of carbonate and the dehydrogenation of CH₄ can be interactively facilitated by the participation of the intermediates produced in each process on the supported Ni-CaO composite catalyst. Specifically, the adsorptive/catalytic interface, which is controlled by balancing the loading density and size of Ni nanoparticles on porous CaO, plays an essential role in the ultra-high CO₂ and CH₄ conversions of 96.5% and 96.0% at 650 °C, respectively.

Highly Cyclic Stability and Absorbent Activity of Carbide Slag Doped with MgO and ZnO for Thermochemical Energy Storage

Carbide slag is a solid waste with a high content of reactive CaO, which can be used as an active material for the chemical absorption of CO₂ and calcium looping. Calcium looping of CaO-based absorbents is one of the most promising methods of thermochemical energy storage. However, the sintering of pores and a reduction in the CO₂ diffusion rates as the carbonization/calcination cyclic reaction progresses have posed challenges to the practical application of CaO-based absorbents. This study proposes a method for alleviating the sintering of the pore structure by improving the activity and cycling stability of such absorbents by doping carbide slag with MgO and ZnO powders. Results showed that the raw material ratio, reaction temperature, and reaction time have a considerable influence on the CO₂ absorption rate. Furthermore, the specific surface area and pore volume of the absorbents increased with increasing ZnO and MgO doping levels in the carbide slag. Thus, the problems of sintering and clogging of pores in CaO-based absorbents were effectively alleviated, and the MgO and ZnO-doped absorbents CMZ85 and CMZ90 maintained 41-42% CO₂ absorption after 10 cycles. These results confirmed that the cyclic stability and absorbent activity improved significantly with the MgO and ZnO doping of carbide slag for the calcium looping process.

Yolk-shell-type CaO-based sorbents for CO2 capture: assessing the role of nanostructuring for the stabilization of the cyclic CO2 uptake

Improving the cyclic CO₂ uptake stability of CaO-based solid sorbents can provide a means to lower CO₂ capture costs. Here, we develop nanostructured yolk(CaO)-shell(ZrO₂) sorbents with a high cyclic CO₂ uptake stability which outperform benchmark CaO nanoparticles after 20 cycles (0.17 g_CO2 g_Sorbent^-1) by more than 250% (0.61 g_CO2 g_Sorbent^-1), even under harsh calcination conditions (i.e. 80 vol% CO₂ at 900 °C). By comparing the yolk-shell sorbents to core-shell sorbents, i.e. structures with an intimate contact between the stabilizing phase and CaO, we are able to identify the main mechanisms behind the stabilization of the CO₂ uptake. While a yolk-shell architecture stabilizes the morphology of single CaO nanoparticles over repeated cycling and minimizes the contact between the yolk and shell materials, core-shell architectures lead to the formation of a thick CaZrO₃-shell around CaO particles, which limits CO₂ transport to unreacted CaO. Hence, yolk-shell architectures effectively delay CaZrO₃ formation which in turn increases the theoretically possible CO₂ uptake since CaZrO₃ is CO₂-capture-inert. In addition, we observe that yolk-shell architectures also improved the carbonation kinetics in both the kinetic- and diffusion-controlled regimes leading to a significantly higher cyclic CO₂ uptake for yolk-shell-type sorbents.

Post-combustion CO2 capture via a variety of temperature ranges and material adsorption process: A review

Carbon dioxide (CO₂) emissions from fossil fuel combustion have been linked to increased average global temperatures, a global challenge for many decades. Mitigating CO₂ concentration in the atmosphere is a priority for the protection of the environment. This is a comparison of the three main technological categories available for CO₂ capture and storage. They include: oxy-fuel combustion, pre-combustion, and post-combustion. Each capture technology has inherent benefits and disadvantages in cost, implementation, and flexibility, but post-combustion CO₂ capture has demonstrated the most promising results in typical power plant configurations. This paper presents a review of different post-combustion CO₂ capture materials; solvents, membranes, and adsorbents, focusing on economical and environmentally safe low to high temperature solid adsorbents. Furthermore, the authors summarize the advantages and limitations of the materials investigated to provide insight into the challenges and opportunities currently facing the development of post-combustion CO₂ capture technologies. The solid sorbents currently available for CO₂ capture are also reviewed in detail, including physical and chemical properties, reactions, and current research efforts on improvement.

Effect of Co-Doping on Cu/CaO Catalysts for Selective Furfural Hydrogenation into Furfuryl Alcohol

Cu/CaO catalysts with fine-tuned Co-doping for excellent catalytic performance of furfural (FAL) hydrogenation to furfuryl alcohol (FOL) were synthesized by a facile wetness impregnation method. The optimal Co_1.40Cu₁/CaO catalyst, with a Co to Cu mole ratio of 1.40:1, exhibited a 100% FAL conversion with a FOL yield of 98.9% at 100 °C and 20 bar H₂ pressure after 4 h. As gained from catalyst characterizations, Co addition could facilitate the reducibility of the CoCu system. Metallic Cu, Co-Cu alloys, and oxide species with CaO, acting as the major active components for the reaction, were formed after reduction at 500 °C. Additionally, this combination of Co and Cu elements could result in an improvement of catalyst textures when compared with the bare CaO. Smaller catalyst particles were formed after the addition of Co into Cu species. It was found that the addition of Co to Cu on the CaO support could fine-tune the appropriate acidic and basic sites to boost the FOL yield and selectivity with suppression of undesired products. These observations could confirm that the high efficiency and selectivity are mainly attributed to the synergistic effect between the catalytically active Co-Cu species and the CaO basic sites. Additionally, the FAL conversion and FOL yield insignificantly changed throughout the third consecutive run, confirming a high stability of the developed Co_1.40Cu₁/CaO catalyst.

Effect of Steam Injection during Carbonation on the Multicyclic Performance of Limestone (CaCO3) under Different Calcium Looping Conditions: A Comparative Study

This study explores the effect of steam addition during carbonation on the multicyclic performance of limestone under calcium looping conditions compatible with (i) CO₂ capture from postcombustion gases (CCS) and with (ii) thermochemical energy storage (TCES). Steam injection has been proposed to improve the CO₂ uptake capacity of CaO-based sorbents when the calcination and carbonation loops are carried out in CCS conditions: at moderate carbonation temperatures (∼650 °C) under low CO₂ concentration (typically ∼15% at atmospheric pressure). However, the recent proposal of calcium-looping as a TCES system for integration into concentrated solar power (CSP) plants has aroused interest in higher carbonation temperatures (∼800-850 °C) in pure CO₂. Here, we show that steam benefits the multicyclic behavior in the milder conditions required for CCS. However, at the more aggressive conditions required in TCES, steam essentially has a neutral net effect as the CO₂ uptake promoted by the reduced CO₂ partial pressure but also is offset by the substantial steam-promoted mineralization in the high temperature range. Finally, we also demonstrate that the carbonation rate depends exclusively on the partial pressure of CO₂, regardless of the diluting gas employed.

Multicycle Performance of CaTiO3 Decorated CaO-Based CO2 Adsorbent Prepared by a Versatile Aerosol Assisted Self-Assembly Method

Calcium oxide (CaO) is a promising adsorbent to separate CO₂ from flue gas. However, with cycling of carbonation/decarbonation at high temperature, the serious sintering problem causes its capture capacity to decrease dramatically. A CaTiO₃-decorated CaO-based CO₂ adsorbent was prepared by a continuous and simple aerosol-assisted self-assembly process in this work. Results indicated that CaTiO₃ and CaO formed in the adsorbent, whereas CaO gradually showed a good crystalline structure with increased calcium loading. Owing to the high thermal stability of CaTiO₃, it played a role in suppressing the sintering effect and maintaining repeated high-temperature carbonation and decarbonation processes. When the calcium and titanium ratio was 3, the CO₂ capture capacity was as large as 7 mmol/g with fast kinetics. After 20 cycles under mild regeneration conditions (700 °C, N₂), the performance of CO₂ capture of CaTiO₃-decorated CaO-based adsorbent nearly unchanged. Even after 10 cycles under severe regeneration conditions (920 °C, CO₂), the performance of CO₂ capture still remained nearly 70% compared to the first cycle. The addition of CaTiO₃ induced good and firm CaO dispersion on its surface. Excellent kinetics and stability were evident.

CO2 Capture at Medium to High Temperature Using Solid Oxide-Based Sorbents: Fundamental Aspects, Mechanistic Insights, and Recent Advances

Carbon dioxide capture and mitigation form a key part of the technological response to combat climate change and reduce CO₂ emissions. Solid materials capable of reversibly absorbing CO₂ have been the focus of intense research for the past two decades, with promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this review, we explore the fundamental aspects underpinning solid CO₂ sorbents based on alkali and alkaline earth metal oxides operating at medium to high temperature: how their structure, chemical composition, and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines, including materials discovery, synthesis, and in situ characterization, to present a coherent understanding of the mechanisms of CO₂ absorption both at surfaces and within solid materials.

Mechanistic Understanding of CaO-Based Sorbents for High-Temperature CO2 Capture: Advanced Characterization and Prospects

Carbon dioxide capture and storage technologies are short to mid-term solutions to reduce anthropogenic CO₂ emissions. CaO-based sorbents have emerged as a viable class of cost-efficient CO₂ sorbents for high temperature applications. Yet, CaO-based sorbents are prone to deactivation over repeated CO₂ capture and regeneration cycles. Various strategies have been proposed to improve their cyclic stability and rate of CO₂ uptake including the addition of promoters and stabilizers (e. g., alkali metal salts and metal oxides), as well as nano-structuring approaches. However, our fundamental understanding of the underlying mechanisms through which promoters or stabilizers affect the performance of the sorbents is limited. With the recent application of advanced characterization techniques, new insight into the structural and morphological changes that occur during CO₂ uptake and regeneration has been obtained. This review summarizes recent advances that have improved our mechanistic understanding of CaO-based CO₂ sorbents with and without the addition of stabilizers and/or promoters, with a specific emphasis on the application of advanced characterization techniques.

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-Ca_0.69Mg_0.3O sorbent, it was tested for 100 carbonation/regeneration cycles of 5 min each under CO₂ lean conditions. The g-Ca_0.69Mg_0.3O sorbent showed exceptional CO₂ capture capacity and cycling stability and retained about 65% of its initial capture capacity after 100 cycles.

Molybdenum carbide and oxycarbide from carbon-supported MoO3 nanosheets: phase evolution and DRM catalytic activity assessed by TEM and in situ XANES/XRD methods

Molybdenum carbide (β-Mo₂C) supported on carbon spheres was prepared via a carbothermal hydrogen reduction (CHR) method from delaminated nanosheets of molybdenum(vi) oxide (d-MoO₃/C). The carburization process was followed by combined in situ XANES/XRD analysis revealing the formation of molybdenum oxycarbide Mo₂C_xO_y as an intermediate phase during the transformation of d-MoO₃/C to β-Mo₂C/C. It was found that Mo₂C_xO_y could not be completely carburized to β-Mo₂C under a He atmosphere at 750 °C, instead a reduction in H₂ is required. The β-Mo₂C/C obtained showed activity and stability for the dry reforming of methane at 800 °C and 8 bar. In situ XANES/XRD evaluation of the catalyst under DRM reaction conditions combined with high resolution TEM analysis revealed the evolution of β-Mo₂C/C to Mo₂C_xO_y/C. Notably, the gradual oxidation of β-Mo₂C/C to Mo₂C_xO_y/C correlates directly with the increased activity of the competing reverse water gas shift reaction.

Development of Magnetic Multi-Shelled Hollow Catalyst for Biodiesel Production

The magnetic CaO-based catalyst has endorsed great enhancements in biodiesel synthesis. In the present work, novel multi-shelled hollow γ-Fe2O3 stabilized CaO microspheres were synthesized using a facile one-step hydrothermal method. The strategy revealed that the well-defined multi-shelled hollow structures were formed with magnetism; the presence of γ-Fe2O3 was the key for the effective structural stabilization, and the multi-shelled hollow structures provided the sites for the active material. The synthesized catalyst was employed for the preparation of biodiesel by transesterification of palm oil and methanol. A four factors response surface methodology was adopted for optimizing the reaction conditions. Ca80Fe20 with a yield of 96.12% performed the highest catalytic activity under reaction conditions of 2 h, a methanol to oil ratio of 12:1, 65 °C and 11 wt. % of catalyst dosage. The catalyst under the optimum transesterification conditions also performed a better recyclability (>85%). In addition, the response surface methodology (RSM) based on the Box–Behnken design was used to optimize the four reaction parameters.

Construction of a hierarchical-structured MgO-carbon nanocomposite from a metal–organic complex for efficient CO2 capture and organic pollutant removal

A hierarchical-structured porous MgO/C nanocomposite derived from a metal–organic complex performs as a remarkable adsorbent for CO₂ adsorption and organic pollutant removal.

Porous spherical calcium aluminate-supported CaO-based pellets manufactured via biomass-templated extrusion-spheronization technique for cyclic CO2 capture

Calcium looping has been proposed as one of the most promising technologies for CO₂ capture to mitigate the growing problem of global warming. However, the loss in capacity and attrition are two issues lying on the way to practical application for calcium looping process. To improve CO₂ capture performance and mechanical strength of CaO sorbents, a biomass templated extrusion-spheronization palletization technique was employed to manufacture porous calcium aluminate-supported CaO-based pellets. For the first time, this work investigated the granulation of calcium aluminate-supported CaO-based sorbents and also the effectiveness of three novel biomass-based pore-creating materials of straw, willow, and wheat. The results indicated that the incorporation of calcium aluminate-based supports could effectively enhance cyclic performance and stability. Besides, the 5 wt.% addition of pore-creating materials could further promote the cyclic CO₂ capture capacity of calcium aluminate-supported CaO-based pellets. The pellets added with 25 wt.% calcium aluminate-based supports and 5 wt.% straw still held a good carbonation conversion of 46.45% after 50 cycles even tested under CO₂-rich calcination atmospheres. In addition, the anti-attrition ability tests by friability tester (FT) demonstrated that all the prepared pellets owned an excellent degree of attrition (less than 1%). The good CO₂ capture performance and mechanical strength endowed biomass-templated calcium aluminate-supported CaO-based pellets with promising prospects for practical CO₂ removal.

Facile synthesis of aminated indole-based porous organic polymer for highly selective capture of CO2 by the coefficient effect of π-π-stacking and hydrogen bonding

A new aromatic aminated indole-based porous organic polymer, PIN-NH2, has been successfully constructed, and it was demonstrated that the coefficient effect endows this porous material with outstanding CO2 absorption capacity (27.7 wt%, 1.0 bar, 273 K) and high CO2/N2 (137 at 273 K and 1 bar) and CO2/CH4 (34 at 273 K and 1 bar) selectivity.

Accurate Control of Cage-Like CaO Hollow Microspheres for Enhanced CO2 Capture in Calcium Looping via a Template-Assisted Synthesis Approach

Herein we report the development of synthetic CaO-based sorbents for enhanced CO₂ capture in calcium looping via a template-assisted synthesis approach, where carbonaceous spheres (CSs) derived from hydrothermal reaction of starch are used as the templates. Cage-like CaO hollow microspheres are successfully synthesized only using urea as the precipitant, and the formation mechanism of this unique hollow microsphere structure is discussed deeply. Moreover, cage-like CaO hollow microspheres possess an initial carbonation conversion of 98.2% and 82.5% under a mild and harsh conditions, respectively. After the 15 cycles, cage-like CaO hollow microspheres still possess a carbonation value of 49.2% and 39.7% under the corresponding conditions, exceeding the reference limestone by 85.7% and 148.1%, respectively. Two kinetic models are used to explore the mechanism of carbonation reaction for cage-like CaO hollow microspheres, which are subsequently proved to be feasible for analysis of chemical-controlled stage and diffusion-controlled stage in the carbonation process. It is found the unique hollow microsphere structure can significantly reduce the activation energy of carbonation reaction according to the kinetic calculation. Furthermore, the energy and raw material consumptions related to the synthesis of cage-like CaO hollow microspheres are analyzed by the life cycle assessment (LCA) method.