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Abstract: Lime mud (LM), a solid waste that results from the causticization reaction in alkali recycling process of paper manufacture industry, was utilized as CO2 sorbent in calcium looping process in this study. The carbonation behavior of LM in the calcination/carbonation cycles was investigated in a dual fixed-bed reactor and a thermo-gravimetric analyzer. The results show that the carbonation conversions of LM are lower than those of limestone at the same reaction conditions. It attributes to the high chlorine content in LM which leads to more pronounced sintering and decreases the CO2 capture performance of LM. A pre-wash process was employed to decrease the chlorine content in LM. Based on an overall consideration of various factors, the pre-wash process is effective enough if the Cl/Ca molar ratio in LM is smaller than 1:100. Pre-washed lime mud (PLM) achieves higher carbonation rates and carbonation conversions, compared with LM. When calcined at 850°C and carbonated at 700°C, the carbonation conversion of PLM maintains at 36% after 100cycles, which is 1.8 and 4.8 times as high as LM and limestone after the same number of cycles, respectively. The pore volume and surface area of calcined PLM were greater than those of calcined LM after the same number of cycles, especially the volume of the pores in the range of 10–100nm in diameter. That is the reason why PLM exhibits higher CO2 capture capacity than LM in the multiple calcination/carbonation cycles. The carbonation conversions of LM and PLM are further enhanced by hydration of their calcines. [Copyright &y& Elsevier]

• Freestanding carbon paper confined with ultrafine lithiophilic TiO 2 is in-situ synthesized from MXene and CO 2. • Freestanding C/TiO 2 paper is firstly employed as dendrite-free Li metal anodic host. • The growth behaviors of metallic Li on C/TiO 2 is systematically probed. • Lithiophilic TiO 2 seeds and conductive 3D carbon synergistically induce dendrite-free Li deposition. • C/TiO 2 @Li paper enables full cell with improved electrochemical performance. Lithium (Li) metal anode is deemed as one of the most fascinating anodes due to its high energy density. Nonetheless, low Coulombic efficiency and safety issues caused by detrimental Li dendrites growth severely hamper its practical application. Herein, we construct an ultrafine TiO 2 confined in 3D freestanding carbon paper by one-step green in-situ oxidation of Ti 3 C 2 T x MXene film with greenhouse gas CO 2. The lithiophilic TiO 2 seeds and freestanding 3D carbon matrix can synergistically induce uniform Li deposition and buffer the volume changes during lithium striping and deposition, which ensure improved electrochemical performance with high Coulombic efficiency and low overpotential, etc. The growth process of metallic Li on C/TiO 2 is also systematically investigated. Moreover, the C/TiO 2 @Li||LiFePO 4 full batteries present a stable cycling performance over 250cycles at 1.0C and superior rate performance. Additionally, this work proposes an alternative way to utilize CO 2 , which may alleviate greenhouse effect and boost sustainable development. These results may be useful for both the design of dendrite-free lithium metal batteries and the sustainable utilizing of CO 2. [ABSTRACT FROM AUTHOR]

Highlights • Synthetic CaO-based CO 2 sorbent was prepared using paper fibre as a biotemplate. • Synthetic sorbent is mainly composed of CaO and Ca 12 Al 14 O 33. • Synthetic sorbents possess microtube-like structure with superior CO 2 uptake. • Synthetic sorbent has improved sintering resistance in severe calcination condition. Abstract Calcium looping is regarded as an effective and viable way to address CO 2 emissions. To overcome the loss-in-capacity problems of calcium-based sorbents with the number of calcium looping cycles, a novel CaO/Ca 12 Al 14 O 33 sorbent with a microtube-like structure was prepared from carbide slag and Al(NO 3) 3 ·9H 2 O using paper fibre as a biotemplate. The CO 2 capture performance and microstructure of the novel synthetic sorbent under calcium looping conditions were investigated. The results show that the utilization of the biotemplate is good to retain the high cyclic CO 2 capture reactivity of the synthetic sorbent. Due to the unique hollow porous structure, the CO 2 capture capacity of the synthetic sorbent containing 7.5 wt% Al 2 O 3 retains 0.56 and 0.33 g/g after 30 cycles under mild and severe calcination conditions, respectively, which are 2.56 and 2.11 times higher than those of carbide slag under the same respective calcination conditions. With the presence of 10% steam in the carbonation atmosphere, the CO 2 capture capacity of the synthetic sorbent retains 0.55 g/g under the severe calcination conditions after 10 cycles. The native hierarchical biostructure of paper fibre is preserved in the synthetic sorbent. CaO and Ca 12 Al 14 O 33 are uniformly distributed in the synthetic sorbent, resulting in a high sintering resistance during multiple CO 2 capture cycles. CO 2 can penetrate through the microtube-like structure of the synthetic sorbent from two directions, i.e., from the outer surface and inner surface. This phenomenon effectively enlarges the contact area between CO 2 and CaO. The CaO/Ca 12 Al 14 O 33 sorbent with a hollow porous structure by means of a biotemplate appears promising in the calcium looping technology for CO 2 capture. [ABSTRACT FROM AUTHOR]

Abstract: The possibility of changing waste paper sludge into valuable carbonaceous adsorbent was tested. The performance of three types of samples obtained from this waste was studied: chars (PK), activated chars (PKA) and activated initial material (PA). Pyrolysis of the initial material was carried out at 550, 600 and 700°C, while the activation of the initial material and chars obtained with CO2 at 550, 600 and 700°C. The sorption capacity of carbonaceous adsorbents obtained was evaluated on the basis of NO2 adsorption in dry and wet conditions. The NO2 sorption properties of the activates decrease with increasing temperature of activation and the maximum sorption capacity was noted for the samples activated at 550°C. On the basis of measurements in dry and wet conditions, the presence of water was found to increase the NO2 breakthrough capacity. The NO2 sorption capacity of the adsorbents obtained depended on the type and temperature of modification process and acid–base properties of the materials obtained. [Copyright &y& Elsevier]

Strategies for changing the conductivity of Li 2 CO 3 is introduced into the fabrication of Li-CO 2 battery. Benefitting from the favorable hierarchical architecture constructed (CPM-MnO 2), facile charge transfer occurs between catalytic surface and Li 2 CO 3 by –OH⋯O hydrogen bonds improves the metallicity of Li 2 CO 3 , facilitating the formation/decomposition of Li 2 CO 3 and bestowing an ultra-long-term stability of 1087 cycles (4348 h). Taking into account its simplicity, scalable character and outstanding performance, this hierarchical composite electrode paves an effective trajectory for the future development of highly efficient cathodes for durable metal-CO 2 batteries. [Display omitted] • Excellent hierarchical structure of MXene and MnO 2 on carbon paper was fabricated. • Enriched charge transfer occurred on MXene and the MnO 2 by OH⋯O hydrogen bonding. • The prepared batteries showed an ultra-long cycle lifetime and low overpotential. • The optimized electronic structure can improve the metallicity of Li 2 CO 3. • The accelerated decomposition of discharge products promoted CRR and CER kinetics. Lithium-CO 2 batteries are recognized as an essential strategy for efficient carbon sequestration and energy storage to achieve carbon neutrality. Their cycle-ability and polarization voltage, however, are hindered by high decomposition voltage (≈4.3–4.5 V) of insulating Li 2 CO 3. Herein, we report a significant advance toward the rational design of self-supporting and ultra-long cycle lifetime cathode for Li-CO 2 batteries, dependence on a favorable hierarchical architecture and rich charge transfer constructed by homogeneously distributed MnO 2 nanoplates rooted in the MXene surface supported by carbon paper. Detailedly, it exhibits impressive ultra-long-term stability of 1087 cycles (4348 h) with a low polarization gap (≈ 0.47 V) at a high current of 200 μA cm−2, which is outperformed by all the liquid electrolyte-based Li-CO2 batteries reported previously. Electronic structure analysis reveals that facile charge transfer occurs between catalytic surface and Li 2 CO 3 , springing from the –OH functional group (in MXene) to MnO 2 by –OH⋯O hydrogen bonds, which acts as charge transfer channels, improving the metallicity of Li 2 CO 3 and facilitating its decomposition and extending battery cyclability. This work paves an effective trajectory for the future development of highly efficient cathodes for durable metal-CO 2 batteries. [ABSTRACT FROM AUTHOR]

[Display omitted] • A bifunctional flexible Pt/TiO 2 -γ-Al 2 O 3 nanofiber paper was successfully prepared. • The PTA sample can efficiently decompose HCHO to CO 2 and H 2 O at room temperature. • PTA1 exhibited better catalytic activity and stability. • The surface coating of TiO 2 in PTA catalyst plays an important role for its performance. • The PTA sample also exhibits good filtration performance for fine particles. A flexible Pt/TiO 2 /γ-Al 2 O 3 nanfiber paper (PTA) was successfully prepared by an electrospinning-coating-NaBH 4 reduction method. The catalytic performance for formaldehyde (HCHO) oxidation over PTA with different Pt contents was investigated at room temperature. The results show that PTA exhibits higher catalytic activity and stability than Pt/γ-Al 2 O 3. The TiO 2 coating can promote the transformation of intermediate species and the desorption of CO 2. The PTA1 with 1 wt% Pt shows the best catalytic activity and good stability. In the view of activity and cost, 0.5 wt% Pt is the optimal Pt content. The TiO 2 coating not only plays an important role in improving the activity and stability of PTA, but also acts as a protective shell of γ-Al 2 O 3 fiber, which greatly reduces the risk of alkali etching during preparation and maintains the good flexibility of PTA. The dioxymethylene (DOM), formate/carbonate species, CO are the intermediate species in HCHO oxidation over PTA. In addition, PTA exhibits good filtration performance for fine particles as well as good fluid permeability. Because of the high efficiency and flexibility of PTA composite catalytic material for HCHO oxidation with good filtration performance for fine particles, it will be a promising candidate in air purification. [ABSTRACT FROM AUTHOR]

• Electroreduction of CO 2 to formate was performed. • Electrooxidation of glucose to formate was performed. • A membrane electrode assembly system that combines CO 2 electroreduction with glucose electrooxidation was presented. • Coupling of CO 2 electroreduction of with glucose electrooxidation generated formate with high efficiency. Electrocatalytic reduction of CO 2 (CO 2 ER) coupled with the oxygen evolution reaction (OER) is an energy-intensive process that generates low-value oxygen, limiting its industrial application. To overcome this limitation, here we report a membrane electrode assembly (MEA) system that combines CO 2 ER with glucose electrooxidation (GEOR) to simultaneously produce formate using bismuth subcarbonate and carbon nanotube hybrid (BOC-CNT) and nickel cobalt oxide decorated on carbon fiber paper (NCO-CFP) as the cathode and anode catalysts, respectively. The BOC-CNT catalyst showed excellent electrocatalytic performance for CO 2 ER to formate, affording a high FE HCOO - of 97.9 % with current density of 360 mA cm−2 at −0.77 V vs. RHE (-580 mV overpotential), and the NCO-CFP catalyst achieved GEOR at 0.99 V (vs. RHE) with FE HCOO - >98 %. The coupled CO 2 ER//GEOR MEA exhibits a low onset cell voltage of 1.20 V and reaches ultrahigh apparent Faraday efficiency of formate (>190 %) in a wide range from 1.8 to 2.4 V, achieving ∼ 33.3 % energy savings compared to CO 2 ER//OER with a high formate yield of 0.92 mol g-1h−1 at 100 mA cm−2. Besides, all generated formate can be collected from the electrolyte on the anode side due to the spontaneous migration of formate under electric field, thus reducing cross-contamination from CO 2 and alkaline electrolytes. In addition, the coupled CO 2 ER//GEOR system exhibited good electrocatalytic stability for at least 32 h. This strategy provides an innovative and promising approach for the co-electrolytic transformation of biomass derivatives and CO 2 to formate. [ABSTRACT FROM AUTHOR]

[Display omitted] • A highly dispersed CuO nano-island anchored Pt catalyst was designed and prepared. • Pt 0.5 -CuO 5 /HMS exhibited 100 % CO conversion (<0.2 ppb) at 110 °C in CO-PROX. • No inactivation was observed for Pt 0.5 -CuO 5 /HMS after 100 h of stability testing. • The adsorption and activation of CO tends to occur at the Pt-CuO interface. • The reaction energy barriers of H 2 on the Pt-CuO interface increased six times. In this paper, a highly dispersed CuO nano-island anchored Pt catalyst is designed and successfully prepared by selective electrostatic adsorption method. It is found that the nano-island catalyst exhibited excellent performance and stability in the CO preferential oxidation reaction. 100 % CO conversion and 50 % CO 2 selectivity are achieved at 110 °C and no indication of decreased efficiency is observed within 100 h. The CO 2 selectivity is constant over the entire temperature range. The characterizations and theoretical calculations are used to investigate the reaction mechanism. The results show that H 2 oxidation tend to occur at the upper surface of Pt clusters which are loaded on the CuO nano-island, whereas the CO oxidation tend to occur at the interface of Pt-CuO. Compared with Pt-Cu bimetallic catalyst, the interface structure of Pt-CuO has been proved to enhance the adsorption and activation of O 2 as well as reduce the energy barrier of CO oxidation from 0.28 eV to 0.01 eV. [ABSTRACT FROM AUTHOR]

• The irreversible adsorption of NPs enhances foam stability. • Synergistic effect of NPs and surfactants on foam stability. • NPs-stabilized foams have good performance under harsh reservoir condition. • NPs-stabilized foams enhance CO 2 storage by blocking macroporous throats. • NPs can reduce the risk of CO 2 leakage. With the urgent need for energy and reduction of carbon emissions around the world, the use of carbon dioxide foam flooding in enhanced oil recovery and CO 2 storage in underground geological structures have received extensive attention. However, as a thermodynamically unstable system, the stability of foam restricts its application in enhancing oil and gas recovery. Nanoparticles can be used as foam stabilizers to enhance the foam stability because of its special properties, thereby improving the effect of oil displacement and storage. Therefore, the use of nanoparticles to stabilize carbon dioxide foam has become a hot topic of current research. In this paper, the mechanism of nanoparticles in enhancing foam stability is reviewed. The effects of nanoparticle type, concentration, size and surface wettability, as well as the environmental factors such as temperature and pressure on stable foams is systematically analyzed. The mechanism of nanoparticles in enhancing carbon dioxide storage is clarified. Finally, the challenges and perspective of nanoparticles to enhance the stability of carbon dioxide foam and assist carbon dioxide storage are proposed, and the future research work is made clear. [ABSTRACT FROM AUTHOR]

[Display omitted] • A philic-CO 2 supercarbon was derived from rice husk waste by a new process. • It possessed the max specific surface area in reported biochars (4230 m2 g−1) • It possessed the max CO 2 uptake capacity in the reported biochars (341.5 mg g−1) • This study gave a new way to generate rich ultra-micropores and C-F groups in char. A super-carbon material as adsorbents of CO 2 were prepared with rice husk waste by a new two-step process, pyrolysis-activation and HF post-desilication process. This paper was focused on investigating the boosting effect and mechanism of post-desilication. It was found that the function of the post-desilication was considerably different from that of the reported pre-desilication. It could not only effectively remove Si element from rice husk biochar (RHC) but also significantly improve its performance, producing a super-biocarbon with a well-developed pore structure, rich C-F groups, and a 4230-m2 g−1 surface area, which is the max surface area of known biocarbon. It could adsorb 341.5 mg g−1 CO 2 , a max CO 2 adsorption capacity of reported biocarbon, and its CO 2 /N 2 and CO 2 /H 2 O adsorption selectivity index reached as high as 22.2 and 2.1, respectively. The large surface area was mainly originated from the expansion effect of SiF 4 gas from the post-desilication, generating numerous ultra-microspores, while these C-F groups were generated by the co-reactions of the post-desilication. The ultra-high adsorption capacity was mainly from the fill-adsorption driven by the size effect of these ultra-micropores and the strong CO 2 -affinity of C-F groups, and the adsorption selectivity was confirmed to depend on water-resistant and CO 2 -philic characteristics of its C-F groups by theoretical calculations and experimental observations. These findings presented not only an advanced CO 2 -capture material but also a facile way to tailor textural structure of other biochars. [ABSTRACT FROM AUTHOR]

• The review discusses progress in the production of C 2+ oxygenates from CH 4 and CO 2 under mild conditions. • The problem of a single active site in the co-conversion of CH 4 and CO 2 can be solved with a multifunctional catalyst. • The effects of the DBD conditions and the catalyst synergy on the conversion and selectivity have been demonstrated. • Optimization of the reaction device is a necessary way to solve the low energy utilization rate. Converting greenhouse gases into C 2+ oxygenates with high-added value is an effective method for reducing carbon emissions. Due to the molecular structure and stability of methane and carbon dioxide, it is difficult to activate the C–H bond and C = O bond which limits the co-conversion of methane and carbon dioxide into C 2+ oxygenates, such as acetic acid and ethanol. The reaction still faces thermodynamic limitations, posing a major challenge in C1 chemical utilization. This paper reviews the literature on the progress of direct conversion of C 2+ oxygenates from CH 4 and CO 2 through thermo- and non-thermal plasma catalysis. It discusses the performance and the corresponding reaction mechanisms over different metal-based catalysts. For thermal catalysis, Cu, Zn, and Pd-based catalysts are the main active metals to generate more active intermediate species and multifunctional catalysts can be prepared to avoid competitive adsorption of two gases. For non-thermal plasma catalysis technology, has the advantage of co-conversion of CH 4 and CO 2 under mild conditions, but the target product selectivity is extremely low which hinders the practical application. Furthermore, the review discusses the impact of the skeleton environment and the promotion of different acid centers on the active center, the influence of the catalyst support, and the optimization of plasma reaction parameters. Facially, the existing challenges and opportunities for the catalyst design and technical route of methane and carbon dioxide conversion to C 2+ oxygenates under mild conditions are summarized. [ABSTRACT FROM AUTHOR]

• Co atomic cluster-anchored and B-doped C 3 N 4 (Co@B-HCN) catalyst was prepared. • Co atomic clusters anchoring enhanced the CO 2 adsorption and activation ability. • Co atomic clusters reduced the overall reaction energy barrier from CO 2 to CO. • The urchin-like porous nanostructure and the B doping favored the charge separation. • The CO yield of Co@B-HCN reached 157.51 μmol⋅g−1⋅h−1, ∼ 22 times that of bulk C 3 N 4. Photocatalytic CO 2 reduction to high value-added fuels and chemicals is a promising strategy for alleviating both energy and environmental crises. However, the poor CO 2 adsorption and activation ability seriously restrict the CO 2 photoreduction activity of metal-free carbon nitride (C 3 N 4), which is an emerging material for photocatalysis applications. In this paper, cobalt (Co) atomic clusters were modified on the surface of hierarchical urchin-like hollow C 3 N 4 nanotubes by NaBH 4 reduction, which endowed the as-designed Co atomic cluster-anchored and B-doped C 3 N 4 (Co@B-HCN) catalyst with strong CO 2 activation and CO 2 photoreduction ability. Theoretical calculations and in situ characterization confirmed that the Co atomic clusters anchoring enabled the change in the bond length/angle of adsorbed CO 2 molecules, as well as the change from a linear model to a bending model. This could enhance the CO 2 adsorption and activation, which played a vital role in reducing the energy barrier of CO 2 -to-CO reaction. In addition, the construction of the hierarchical urchin-like nanostructure, the anchoring of Co atomic clusters, and the doping of B favored the surface adsorption and charge separation. Attributed to the above merits, the CO yield of Co@B-HCN photocatalyst reaches 157.51 μmol⋅g−1⋅h−1, which is approximately 22 times that of bulk C 3 N 4. This work provides an insight for the surface engineering of C 3 N 4 photocatalysts to realize high-performance photocatalytic CO 2 reduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simultaneously realized the value-added conversion of greenhouse gas CO 2 and natural gas. • C 2 H 4 selectivity reached 82.7 % on 2 % Ti-substituted Fe 1.5 Ni 0.5 /CeTi-C-2 catalyst. • The substitution of Ti induces the generation of oxygen vacancies O v to promote the reaction. • Activation energy barrier of CO 2 on Ti-CeO 2 (111) decreased from 3.87 eV to 2.17 eV. The catalytic reaction of CO 2 with ethane balances the resourceful conversion of CO 2 and the value-added utilization of shale gas. In this paper, the effects of different metal cation substitutions on CeO 2 support in Fe-Ni catalysts on the regulation of CO 2 and ethane directional catalytic reaction performance were studied through experiments combined with DFT calculation simulations. It was found that the Ti-substituted Fe 1.5 Ni 0.5 /CeTi-2 catalyst had the highest ethane conversion of 11.8% and CO 2 conversion of 21.2%, and presented a high-value product C 2 H 4 selectivity higher than 80%. The Ti/La species in the substituted structure are highly dispersed into the CeO 2 lattice to form a Ti/La x Ce 1-x O 2−δ solid solution, which induces more (-111) and (110) crystal planes with high ethylene selectivity. The Ti-substituted catalyst has the highest proportion of Ce3+, which improves the formation and transfer of active oxygen, making Fe 1.5 Ni 0.5 /CeTi-C-2 exhibit higher catalytic reactivity. The substitution of metal cations weakens the adjacent Ce-O bond strength, and the Ti substitution structure facilitates the generation of O v as a highly active center for CO 2 reduction, resulting in a decrease of the energy barrier for the CO 2 dissociation process from 3.87 eV on pristine CeO 2 (111) to 2.17 eV, and the reaction energy endotherm is 1.03 eV. Both kinetically and thermodynamically, the reduction dissociation of CO 2 on Ti-CeO 2 (111) is more competitive than that on Zr and La-substituted CeO 2 (111). [ABSTRACT FROM AUTHOR]

[Display omitted] • Migration regulation of Ca2+ species in the CaNaX zeolite was revealed in detail. • Utilization of hydroxylated Ca2+ species in the supercages of CaNaX zeolite was maximized via low-temperature calcination. • Remarkable CO 2 uptakes and selectivity on the 0.05CaNaX-250 zeolite were achieved. • This new sorbent displayed low heat of adsorption, fast kinetics and superior recyclability. • The formation of Ca(OH)+∙∙∙(CO 2) 2 adducts revealed by CO 2 -dosing FTIR experiments. Ca-FAU zeolite sorbents have been recognized as one of promising CO 2 capture materials, while it is subject to the change in the speciations and locations of Ca2+ species as adsorption sites in the FAU zeolite due to its susceptible migration. In this paper, a facile strategy is reported by tuning calcination temperatures and Ca loadings, to maximize the utilization of Ca2+ species in the supercages of CaNaX zeolites. Detail characterizations of TG-MS, in situ FTIR spectroscopy and XRD Rietveld refinement reveal the changeable regular in the chemical speciations, locations and number of Ca2+ species in the CaNaX zeolites. Synthetic 0.05CaNaX-250 zeolite (calcined at 250 °C and Ca loading of 1.58 wt%) guarantees at least 21 Ca(OH)+ species (depicted as hydroxylated Ca2+ species) in the supercages per FAU cell unit, close to theoretical value. Such sorbent apparently improves the CO 2 uptakes and the separation from CO 2 /N 2 and CO 2 /CH 4 , along with fast kinetics, low heat of adsorption, measured by dynamic and gravimetric adsorption methods, respectively. In addition, it keeps a superior recyclability after 10 times regeneration. CO 2 -dosing FTIR experiments further illustrate that excellent CO 2 adsorption performance are benefited from the formation of Ca(OH)+∙∙∙(CO 2) 2 adducts with an appropriate interaction. This work is of great significance to better understand the role of cations in FAU zeolites, and also provides an important reference value for the directional design of effective adsorption sites in other excellent CO 2 zeolite sorbents. [ABSTRACT FROM AUTHOR]

[Display omitted] • 0.25% Ru DFM supported on a monolith demonstrated stability over 250 h of aging at varying ambient CO 2 capture conditions. • Ru catalyzes methanation and the decomposition the Na 2 CO 3 sorbent precursor to highly dispersed "Na 2 O" on Al 2 O 3. • Lower Ru% (<0.25 %Ru) DFM monolith will decrease material costs but with some small penalty in performance. Dual function materials (DFMs) comprised of 0.25 %Ru, 6.1 %Na 2 O/γ-Al 2 O 3 //monolith were evaluated for about 250 hours time-on-stream (TOS) at various simulated ambient climate capture conditions followed by temperature swing methanation to 280 °C. This paper focuses on the impact of thrifting Ru to low levels and the impact on performance. Results showed both stable CO 2 capture capacity and CH 4 production with 0.25 % Ru DFM deposited on a ceramic monolith. The CO 2 conversion to CH 4 production was decreased slightly by the Ru decrease from 1 % to 0.25 %. The capture capacity decreased since a lower Ru content reduces the complete decomposition of the Na 2 CO 3 precursor producing fewer active adsorption sites ("Na 2 O"). The deployment of a low Ru DFM monolith would significantly decrease the overall capital cost and give more potential for a large-scale direct air capture and methanation (DACM) application. [ABSTRACT FROM AUTHOR]

• The performance parameters of five benchmark DAC adsorbents in seven aspects were determined by experiments. • A set of comprehensive evaluation methods that can be applied to different types of adsorbents was provided. • The performance parameters of state-of-the-art DAC adsorbents were summarized and analyzed. • Suggestions on the current characterization methods of DAC adsorbents in different aspects were provided. Direct air capture (DAC) of carbon dioxide has been identified as a necessary negative emission technology to limit global temperature rise to 2 °C by 2100. With the research progress in DAC, an increasing number of adsorbents have been developed and investigated. This brings about the questions that what makes good adsorbents for DAC and how to characterize and compare them with different natures. In this paper, the performance parameters of state-of-art DAC adsorbents were investigated, and it is found that because of the varying test conditions, the comparison of some parameters appears to be difficult. Therefore, it is recommended that for each performance parameter, it is best to determine relatively uniform test methods. To this end, this paper selected five benchmark adsorbents and used a set of test methods as a demonstration. Key performance parameters of the adsorbents were measured. On this basis, by comparing the results with that in existing research, the characteristics of different types of adsorbents were summarized and suggestions for future material development were provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • Amines displayed dual functions as an alkaline reagent and the CaCO 3 regulator. • Remarkable CO 2 removal (>95 %) and CO 2 capacity (>340 g /kg) were obtained. • Promising gypsum conversion (>93 %) were obtained. • Primary/secondary amines postponed the formation of CaCO 3 and induced vaterite. • Amines were regenerated from their protonated forms by BMED. CO 2 mineralization of waste gypsum not only reduces the carbon emissions of power plants but also improves gypsum utilization by recovering high-value-added CaCO 3. However, the extensive consumption of various reagents limited its development. This paper proposed an amine-promoted waste gypsum carbonation process integrating with amine regeneration by bipolar membrane electrodialysis (BMED). The alkaline amine was expected to act as a multifunctional reagent for gypsum carbonation — alkaline reagent, CO 2 absorbent, gypsum dissolution promoter, and CaCO 3 crystal regulator. Seven typical amines with different amino types and p K a values were selected to investigate the feasibility of this process. Results show that promising CO 2 removal efficiency (>95 %) from an artificial exhausting gas, gypsum carbonation efficiency (>93 %), and CO 2 sequestration capacity (>340 g-CO 2 /kg-gypsum) can be achieved due to the additional alkalinity, fast CO 2 absorption, high CO 2 concentrations, and enhanced CaSO 4 dissolution in amine solutions. In addition, the interactions of amine-CO 2 -gypsum and the CaCO 3 growth mechanism in the gas–liquid-solid system were explored. Monoethanolamine (MEA), 3-amino-1-propanol (MPA), piperazine (PZ), and 1,3-Diaminopropane (DAP) could prolong the CaCO 3 precipitation due to their strong affinity for Ca2+ and CO 3 2−. In this case, CO 2 absorption by the liquid phase dominated the carbonation process in the initial 30 min for these four amines, while CaCO 3 precipitation mainly occurred within 30 ∼ 120 min. Amines' different affinities for Ca2+ and CO 3 2− provided an approach to selective synthesis of CaCO 3 polymorph: 100 % calcite by PZ, 100 % vaterite by DAP, a calcite-vaterite mixture by MEA, and a calcite-vaterite-aragonite mixture by MPA. After the carbonation process, amines were recycled from the liquid residue by BMED, which could provide OH− for amines regeneration from protonated amines, recovery of H 2 SO 4 , and decrease the solution salinity. [ABSTRACT FROM AUTHOR]

Mesoporous FeAlOx based catalysts were designed through framework-confined strategy for the oxidative dehydrogenation of 1-butene with CO 2. Framework-confined catalyst improved the mobility of oxygen species and released more active oxygen species, and thus 1-butene conversion and 1, 3-Butadiene (BD) selectivity increased. Cr and Ca doped could improve the basicity of the catalyst and had a higher utilization rate of CO 2. [Display omitted] • A framework-confined strategy was used to effectively improve the lattice oxygen. • The doping of Cr species could effectively improve the stability and reduce the coke formation. • The doping of Ca species could effectively improve the basicity of the catalyst and the utilization rate of CO 2. The activation of oxygen species is always a challenging problem in the oxidative dehydrogenation (ODH) of 1-butene with CO 2. The oxygen species play an important role in improving the conversion, yield, selectivity, and stability of FeAlO x -based catalysts. In this paper, the framework-confined (FC) strategy was used to active the oxygen species. The changed crystalline phase from Fe 2 O 3 to FeAlO 4 illustrated the introduction of Fe species destroyed the Al 2 O 3 lattice and more active oxygen species were released. Compared with the WI-Fe 2 O 3 /Al 2 O 3 samples, the ratio of active lattice oxygen was increased from 0.03 to 0.1 and the ratio of Fe3+ was also increased from 0.63 to 0.76 in the FC-FeAlO x samples. After doping with other metal species, the ratio of active lattice oxygen was further increased. The 1-butene conversion could reach 80 % and the 1, 3-Butadiene selectivity could reach 33 % over the FC-FeCrAlO x samples. Besides this, the FC-FeCrAlO x samples showed an outstanding thermal stability, which might be caused that Cr species could reduce the coke formation. The FC-FeCaAlO x samples had a higher utilization rate of CO 2 , which might be caused that Ca species could improve the basicity of the catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] Metal-free, halogen-free heterogeneous catalysts efficiently convert CO 2 to cyclic carbonates under solvent-free and co-catalyst-free conditions. • Novel UM-OP and AM-OP with rich N sites and –NH- groups were facilely synthesized. • UM-OP and AM-OP are metal- and halogen-free, can catalyze CO 2 without co-catalyst. • UM-OP is easily separated and shows good stability, recyclability and versatility. • DFT proves that N sites can adsorb and activate CO 2 and can act as nucleophiles. • DFT shows that double –NH- activate epoxides is stronger than single –NH- groups. The development of highly efficient and metal- and halogen-free heterogeneous catalysts for the chemical conversion of CO 2 to cyclic carbonates plays a critical role in the reduction of greenhouse gas emissions. Herein, two melamine-based organic polymers namely UM-OP and AM-OP with abundant N sites and –NH- groups were synthesized by a facile method and their activity for cycloaddition of CO 2 with epoxides was investigated. The structural analysis shows that the UM-OP and AM-OP catalysts were composed of specially designed urea and amide group linkages, respectively. UM-OP and AM-OP are metal-free, halogen-free, and can efficiently catalyze CO 2 cycloaddition under solvent-free and cocatalyst-free conditions. Moreover, the UM-OP catalyst exhibited higher catalytic activity than AM-OP, good structural stability, recyclability, separability from the products, and shown high activity to a series of epoxides. The density functional theory (DFT) calculations revealed the activation of epoxides by –NH- groups and CO 2 by N sites in the samples, respectively, and N sites can also act as nucleophiles to realize ring opening of epoxides. Combining the results of experiments and calculations, it was further found that the double –NH- (urea group) is more efficient than single –NH- (amide group) to activate the epoxides. This paper reveals the mechanism of N sites and –NH- groups synergistically catalyzing the CO 2 cycloaddition, and further supports the theory that N atoms acts as nucleophile for ring opening, providing a reference for the design of metal- and halogen-free heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • A profound understanding of single atom catalysts (SACs) for electrocatalysis application. • The advantages of MXene supports in SACs for electrocatalysis are established. • MXenes offer structural tailoring for various elements during synthesis or post synthesis. • The application of MXene-based nanocomposites catalyst for CO 2 RR, OER, HER, are highlighted. High atomic utilization of single atom catalysts (SACs) have the advantages of high catalytic performance and high selectivity. The characteristics of "independent active site" and "easy recycling" of heterogeneous catalysts can effectively solve the deficiencies of precious-metal catalysts for energy conversion applications. However, to get the full advantages of SACs, the role of anchoring sites and supports is critically significant. The anchoring supports enhanced the stability of isolated atoms as well as affected its electronic assembly, thereby affecting the catalytic performance. MXenes are emergent new 2D materials with the characteristics of high specific surface area, adjustable band gap, good conductivity and rich chelating sites, an ideal support material for SACs. This paper briefly summarized the structural characteristics of MXene, reviewed the preparation strategies of MXene-based SACs, and emphasized the energy conversion applications of MXene-based SACs by discussing the small molecular reactions, including O 2 /H 2 evolution reaction, O 2 /CO 2 /N 2 reduction reactions as well as bi-functional SACs for the water-splitting and rechargeable metal-air batteries. Finally, the current challenges and opportunities are summarized in synthesis of MXene-based SACs and energy conversion applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel way to perform dry-reforming of methane under dynamic operation. • Stability is enhanced compared to steady state operation with negligible deactivation over 50 cycles. • The reaction mechanism involves fast coking which is dynamically decomposed. • The process allows intrinsic separation of CO and H 2 products and tuning CO:H 2 ratio. • La-promoted Ni/ZrO 2 catalyst shows remarkable conversion of CH 4 (99%) and CO 2 (96%). Dynamic coke-mediated dry reforming of methane (DC-DRM) is an unsteady-state strategy to overcome the limitations of co-feed operation, including the fast deactivation of the catalysts and the loss of valuable H 2 in the reverse water gas-shift reaction. This paper proves the feasibility of DC-DRM on Ni-based catalytic systems, identifying suitable metal oxides supports and evaluating the role of metallic promoters. A La-promoted Ni/ZrO 2 catalyst exhibited excellent and stable catalytic performances at 800 °C approaching complete conversion of the CH 4 and CO 2 reactant pulses in the reaction loop, and separation of the H 2 and CO product streams. Adding the redox functionality of reducible oxides (TiO 2) in the catalyst support is demonstrated as a powerful tool to enable direct formation of syngas in the methane pulse with control on the H 2 /CO ratio. [ABSTRACT FROM AUTHOR]

[Display omitted] • An innovative bioinspired CO 2 sorbent was synthesized by pyrocatechol and HMDA; • Outstanding CO 2 capture of 7.28 mmol/g was achieved under 4% humidified CO 2 at RT; • Easy functionalization for higher CO 2 capture and lower energy penalty regeneration. • Mussel-inspired coatings were completely stable over 50 adsorption/desorption cycles; • Our coating approach can be potentially applied to a plethora of surfaces. Nowadays, finding innovative technologies to efficiently adsorb/desorb CO 2 over several cycles with low energy consumption is a pressing environmental concern. In this work, a new bioionspired coating based on the copolymerization of benzene-1,2-diol and hexamethylenediamine, with a CO 2 uptake of 7.28 mmol/g under humidified conditions with an outstanding chemical stability and regenerability process is reported. Further functionalization with glycidyltrimethylammonium chloride increases the uptake capacity up to 9.96 mmol/g while lowering the desorption temperature down to 50 °C for 20 min. Moreover, the coating shows strong adhesion on cotton and paper, without modifying their intrinsic permeability and mechanical properties, allowing for the recycling of fully available and environmentally friendly biomass. These results demonstrate the competitive advantages of this bioinspired coating compared with current technologies to capture CO 2 while accomplishing the resource efficiency of bioeconomy policies. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new method for the identification of the best reaction concept from an overall process point of view is proposed. Using this method the optimal reaction route is determined independent of existing apparatuses and the recycle affecting the reactor is fully considered. The reaction concept and the design parameters of the process are simultaneously optimized. For this purpose, a detailed model of the reaction system including reaction kinetics, thermodynamic relationships, and intrinsic boundaries such as explosion limits as well as a complete model of the downstream process is set up. The potential of different reaction concepts including innovative process intensification alternatives can easily be determined by comparison with an optimized reference case. The example considered in this paper is the oxygen based ethylene oxide process, which is one of the most important chemical bulk processes. Sophisticated cooling in combination with distributed oxygen dosing along the reactor length is identified as best technical reaction concept with a potential of reducing the operating costs of an average sized plant by 1.35Mio$/a compared to an optimized reference case. In addition, the utility consumption is reduced, especially the consumption of electricity is decreased by 46.3%, and the overall CO2 emissions are cut by 8%. In conclusion, the proposed method enables the predictive determination of the best reaction concept from an overall process point of view taking the full interconnections between the reaction concept and the process into account and considering highly innovative process intensification options. Thereby, this method provides a key stone for the development of more economical and more sustainable chemical reactors and processes of the future. [Copyright &y& Elsevier]

Abstract: This paper is collocated after two other works in which sieved or demineralized coal combustion ashes were used as cadmium (Cd2+) sorbent for water treatments, and the changes in raw ash properties were followed upon steam- and CO2-gasification. In the present paper, ash samples activated by steam- or CO2-gasification were used to adsorb Cd2+ in model aqueous solutions, to elucidate the relationships among ash properties, gasification treatments, properties of the gasified ash and its sorption behavior. To this end, equilibrium and kinetic cadmium adsorption tests were carried out using the gasified ash (treated with either steam or CO2) as sorbent and under fixed operating conditions (for example, the contact time was 7days and the initial Cd2+ concentration in the aqueous solution to be treated varied between 5 and 50mgL−1 for equilibrium tests, while kinetic tests were carried out for times ranging from 10min to 7days using an initial Cd2+ concentration equal to 50mgL−1). Results were expressed in terms of adsorption isotherms, removal efficiency and kinetic curves. Post-processing of experimental data allowed to provide estimations of relevant parameters such as the equilibrium and the kinetic constants, the separation factor, the initial adsorption rate, the characteristic adsorption time. Besides a direct confrontation between the two gasification treatments, results were also compared with former experiments on the same raw material, and with the main outcomes emerging from the pertinent literature, confirming that the gasified materials resulted as very attractive sorbents for Cd2+ capture from wastewaters. [Copyright &y& Elsevier]

Abstract: Previously, it was found that precipitating CaCO3 through the carbonation route by bubbling carbon dioxide using a microbubble generator (MBG), as opposed to a conventional bubble generator, reduces the acquisition time. However, the physical properties of the precipitated CaCO3 (polymorph:calcite) using MBG have not been clarified. The physical properties of CaCO3 determine its usefulness in diverse fields. Therefore, this study investigated the specific surface area and size of primary and secondary calcite particles obtained using MBG. These properties were found to be affected by the Ca(OH)2 concentration, CO2 injection rate, and electrolyte dose in the suspension supplying the calcium ions. Comparison with control experiments using a conventional bubble generator showed that the particles obtained using MBG are smaller and have a greater specific surface area. The fine calcite particles with large specific surface area obtained by the additive-less precipitation using MBG are expected to be applied to the removal of acidic gas, such as sulfur dioxide, and as a paper making filler. The low cost and high CO2 consumption efficiency afforded by the MBG also make it promising for carbon capture and utilization. [Copyright &y& Elsevier]

Abstract: A different approach is presented for the operation of seawater RO desalination plants in which the boron concentration in the product water should not exceed 0.3mgB/l. The approach is based on strong acid (either H2SO4 or HCl) dosage to the feed water to attain pH∼4.3, followed by CO2 stripping and subsequently strong base addition to pH 9.00–9.25. At this high pH range, a high B removal efficiency is attained, and since the water is practically devoid of carbonate species, no CaCO3(s) scaling takes place, and pH elevation is limited by Mg(OH)2(s) precipitation, expected only at pH>9.45. The approach enables operation in the absence of antiscalants. Furthermore, CO2 stripping is effected in stripping towers in two steps: the high CO2(aq) concentration is first stripped by vacuum-operated stripping towers and the CO2-rich air is used for dissolution of calcite in the post treatment stage. The remaining CO2 mass is stripped to the atmosphere using blower-assisted stripping towers. This paper aims at introducing the new concept and providing “proof of concept”. The paper addresses experimental and theoretical aspects of the proposed process, as well as engineering and economic evaluation. The proposed approach is shown to be both technically feasible and cost effective, as compared with conventional boron removal alternatives. [Copyright &y& Elsevier]

Abstract: This work deals with the regeneration of a KOH solution to use in a chemical absorption process for biogas upgrading. The proposed method consists in the caustic recovery of the spent absorption solution by carbonation of selected industrial residues and allows to store the separated CO2 in a solid phase (calcite). This paper presents the main results of the lab scale experiments carried out to evaluate the effects of selected operating parameters on the carbonation reaction so to identify the conditions that allow to maximize the CO2 uptake of the solid residues and the percentage of KOH that can be regenerated for the absorption process. Furthermore, the effects of the tested treatments on the leaching behavior of the residues are also examined. The results presented in this paper were obtained within the UPGAS-LOWCO2 project (LIFE08 ENV/IT/000429) funded by the European Commission. [Copyright &y& Elsevier]

Graphical abstract Highlights • A facile approach to prepare N-doped carbon materials was developed. • N-doped biochar was synthesized by simply ball milling pristine biochar with NH 3 ·H 2 O. • NH 2 and C N were loaded on biochar through the dehydration of COOH and OH. • N-doped biochar showed enhanced sorption for CO 2 and reactive red in comparison to N-free biochar. Abstract Doping of nitrogen (N) on carbon materials often requires complicated synthetic steps or specific machinery. In this study, N-doped biochar was successfully synthesized by simply ball milling pristine biochar with ammonium hydroxide. The content and species of N in the resulting N-doped biochars were carefully characterized, the formation mechanisms of N-related groups were illustrated, and their applications in CO 2 uptake and reactive red removal were evaluated. Most of N introduced to biochar was loaded on its surface in forms of NH 2 and C N, resulting from the dehydration of COOH and OH. Biochars produced at 450 °C were doped with more N on the surface (XPS, 2.41%–2.65%) than those produced at 600 °C (XPS, 1.18%–1.82%) because the content of O-containing functional groups in biochar decreases with increasing pyrolysis temperature. The basic properties of N-related groups enhanced the sorption performance of biochar to both acidic CO 2 and anionic reactive red. For example, the CO 2 uptake of the N-doped, 450 °C hickory biochar was 31.6%–55.2% higher than the corresponding pristine and ball-milled biochars. The maximum sorption capacity of the N-doped, 600 °C bagasse biochar to reactive red was about 3.66–16.2 times of the corresponding biochars without N doping. This paper provides an alternative and facile approach to prepare N-doped biochar that can be extended to other carbon materials to meet the specific needs in different applications, especially adsorption. [ABSTRACT FROM AUTHOR]

Abstract: Dimethyl ether (DME) has been discussed as a potential fuel for both combustion and fuel cell applications. This paper evaluates the ability for membranes to separate DME from syn-gas components, such as H2 and CO. Separations from CO2 and CH4 also are discussed. Experiments performed include permeability and selectivity of these gases through poly(4-methyl-1-pentene) (TPX) and poly(dimethylsiloxane) (PDMS) using variable temperature mixed gas experiments. The DME data is the first to be reported through these membranes. In this paper, the chosen polymers reflect both rubbery and semicrystalline materials. Rubbery polymers tend to be weakly size sieving, which, in this work, has resulted in larger permeabilities, lower separation factors, and lower activation energies of permeation (E p). Conversely, the semicrystalline TPX membranes showed much greater sensitivity to penetrant size; although the gas condensability also played a role in transport. [Copyright &y& Elsevier]

Abstract: Carbonyl sulfide represents an undesirable impurity in a variety of industrial gases and it has to be removed down to very low concentrations to meet the required specifications. This can be achieved by chemisorption with alkanolamines. In this article, the kinetics of the reaction of carbonyl sulfide with alkanolamines is reviewed. Different reaction mechanisms used to interpret experimental kinetic data, viz. zwitterion, termolecular and base-catalysed hydration are described in detail. The kinetic behaviour of several conventional, sterically hindered, cyclic amines and diamines proposed in the literature is analysed. Generally, the reaction of carbonyl sulfide with primary, secondary and sterically hindered amines is described by the zwitterion mechanism, whereas the reaction with tertiary amines is described by the base-catalysed hydration of carbonyl sulfide. The same reaction pathways are followed by carbon dioxide which is similar in structure to carbonyl sulfide. While the carbon dioxide reaction with alkanolamines has been comprehensively reviewed, e.g., in our recent paper (P.D. Vaidya, E.Y. Kenig, CO2–alkanolamine reaction kinetics: a review on recent studies, Chem. Eng. Technol. 30 (2007) 1467), an overview on the kinetic behaviour of carbonyl sulfide is still missing. In this paper, an evaluation of the published results is given to close this gap. [Copyright &y& Elsevier]

[Display omitted] • The influence of the compositions and structures of Cu-ZrO 2 catalysts is explored. • Oxygen vacancy on the ZrO 2 surface play an essential role in CO 2 activation. • Methanol selectivity is mainly affected by low-valence Cu species and ZrO 2 interface. • In addition the interface, the pore size also has an effect on CH 3 OH selectivity. • DFT calculations also emphasize the roles of oxygen vacancy and the formate pathway. In this paper, Cu-ZrO 2 catalysts were prepared and used for CH 3 OH synthesis through CO 2 hydrogenation to clarify the influence of their compositions and structures on the catalytic performance. We mainly address the problem that how the oxygen vacancy and Cu-ZrO 2 interface affect the catalytic performance jointly, because the previous articles only pay attention to the influence of the interface on CH 3 OH synthesis. Combined with experiments and various structural characterizations, we propose that oxygen vacancies play an essential role in CO 2 activation instead of the interface; CH 3 OH selectivity is determined by the low-valence Cu species (Cu0 and Cu+) and ZrO 2 interface (the main factor), and the pore size. The in-situ DRIFTS demonstrates that the conversion of *HCOO active intermediates to *CH 3 O on the optimal catalyst (CuZr-1) is faster. DFT calculations also shed light on the importance of oxygen vacancy in CO 2 adsorption and the formate pathway. We believe this work provides useful insight for researchers to design highly efficient Cu-based catalysts for CO 2 hydrogenation to CH 3 OH. [ABSTRACT FROM AUTHOR]

[Display omitted] • The restructuring and degradation of OD-Cu during CO 2 reduction were revealed. • The C 2 + FE of OD-Cu decreased from 39.4% at 1 h to 26.0% at 5 h at −1.5 V vs. RHE. • Cu defect sites are easily dissolved during electrochemical CO 2 reduction. • Low-coordinated Cu defect sites are responsible for CO 2 reduction to C 2+ products. • The degradation can be circumvented and the FE of C 2+ products maintained at ca. 47.2% with the Cu redeposition process. Renewable energy produced through electrochemical CO 2 reduction is promising for mitigating the energy crisis and environmental issues. Notably, oxide-derived copper (OD-Cu) has attracted considerable attention owing to its unique ability to catalyze CO 2 electroreduction to >2e− products, especially C 2+ products, which are the key feedstocks for the chemical process. However, Cu under operating conditions usually leads to structure reconstruction and degradation, which hinders understanding the origin of its activity. Understanding the restructuring and degradation of OD-Cu catalyst to form C 2+ products is critical for understanding the active sites and, thus for designing effective and durable catalysts for CO 2 reduction. This paper describes that Cu defect sites are easily dissolved during electrochemical CO 2 reduction, and the presence of defect sites is strongly related to the catalytic performance of C 2+ products. Here, the C 2+ products Faradaic efficiency (FE) of OD-Cu decreased from 39.4% at 1 h to 26.0% at 5 h at −1.5 V vs. RHE, along with a decrease in low-coordinated defect sites. The low-coordinated defect sites facilitate CO adsorption and help to increase the CO coverage, thus promoting CO–CO coupling. The decrease in the number of defect sites and activity degradation is circumvented by promoting the Cu redeposition process. The C 2+ products FE of OD-Cu can be maintained at ca. 47.2% without an obvious decrease in CO 2 -saturated 0.1 M KHCO 3 with 1 mM Cu2+. The results of this study help in understanding the activity of OD-Cu and reveal its deactivation mechanism. This knowledge will aid in designing highly active and stable catalysts for CO 2 reduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hierarchical porous Mg-MOF-74 was synthesized by weak coordination of Cl−. • The mesoporous content of hierarchical porous Mg-MOF-74 reached 34.90%. • The CO 2 saturated adsorption capacity increased by 15% at ambient pressure. • The IAST selective adsorption performance of CO 2 /N 2 increased by 20 times. • The adsorption capacity and rate of low pressure were improved. Adsorbents with high adsorption capacity and high selectivity are crucial for carbon capture, utilization and storage (CCUS) technology applied to industrial flue gas to reduce carbon emissions. In this paper, a defect-rich hierarchical porous Mg-MOF-74 was synthesized successfully with MgCl 2 ·6H 2 O used as a metal source considering that the weak coordination of Cl− may interfere with the normal coordination process of metal centers and organic ligands, which causes the formation of crystal defects. Through the analysis of a series of characterizations, ligand deletion of Mg-MOF-74 prepared with MgCl 2 ·6H 2 O was confirmed, and the deleted ligand was estimated to be approximately 20% compared with the traditional Mg-MOF-74 prepared with Mg(NO 3) 2 ·6H 2 O, which led to mesopores accounting for 36.9%, and the width of mesopores reached 13.1 nm. Compared with traditional Mg-MOF-74, the adsorption heat of CO 2 at zero load of the defect-rich hierarchical porous Mg-MOF-74 increased from 36 kJ·mol−1 to 46 kJ·mol−1, and the saturated adsorption capacity of CO 2 under ambient pressure was improved by 15%. Interestingly, the IAST selective adsorption performance of CO 2 /N 2 was increased by 20 times. Compared with the saturated adsorption capacity for traditional Mg-MOF-74, the equivalent adsorption capacity of hierarchical porous Mg-MOF-74 only needs 17 kPa, indicating that it is suitable for carbon capture operation in a real flue environment. Calculations of density functional theory (DFT) confirmed that the active site of the hierarchical porous Mg-MOF-74 has a lower adsorption energy with CO 2 due to the presence of defects, which is regarded to play a key role in improving the CO 2 capture performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • The output data and potential of industrial solid wastes for CO 2 mineralization are analyzed. • The limitation reasons of CO 2 mineralization for industrial applications are found. • The huge energy and cost consumption is the biggest block for its progress. • The approaches for reducing energy and cost consumption are reviewed. CO 2 mineral carbonation is a promising strategy to abate global warming. However, its industrial applications were still limited. This paper reviews the current developments of mineral carbonation technologies by using industrial solid wastes as feedstocks, aiming at searching the reasons of its limitation. Firstly, the pathways and principles for CO 2 mineral carbonation are briefly introduced. Then, the carbonation potential and processes of the most representative and available industrial solid wastes are summarized and compared. Iron and steel slags exhibit great potential due to their high alkali content and reactivity. Based on the preliminary economic analysis, the reasons for the limitation of current scale-up applications of CO 2 mineral carbonation are the concerns of energy and cost consumption. The process parameter optimization and equipment design for scale-up applications need to be extensively investigated. Meanwhile, the recovery of high-value products during the carbonation process improves the economy and make the process more promising for industrial applications. The feasibility for recovering various value-added byproducts such as precipitated calcium carbonate (PCC) and zeolites was reported and discussed in this paper. Lastly, two research directions, i.e. the evaluation of CO 2 net emission reduction by life cycle assessment technique and developments of new energy-saving approaches, are suggested. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Mg/DOBDC MOF@GO composite was fabricated for dynamic CO 2 capture. • The obtained Mg/DOBDC MOF@GO w-30 showed high dynamic CO 2 uptake of 8.60 mmol g−1. • A comprehensive investigation of the novel Mg/DOBDC MOF@GO composite was discussed and summarized. In this paper, Mg/DOBDC MOF (a MOF built of Mg (II) ions linked by 2,5-dioxido-1,4-benzenedicarboxylate (DOBDC) ligands) was first used as the precursor to fabricate a novel Mg/DOBDC MOF and graphene oxide (GO) composite (Mg/DOBDC MOF@GO). A comprehensive investigation of CO 2 capture performance of the novel synthesized Mg/DOBDC MOF@GO composite was discussed and summarized. Initially, the influence of preparation method, the solvent of GO and the ratio of GO in the composite was systemically investigated. Following, the structure change of the Mg/DOBDC MOF after introducing of GO was thoroughly studied. Finally, the cyclability, kinetic study and adsorption mechanism were also discussed. The obtained Mg/DOBDC MOF@GO w-30 with 30 ml GO showed the maximum CO 2 uptake of 8.60 mmol g−1 at 0.1 MPa and 25 °C, which is almost twice as much as the parent Mg/DOBDC MOF. This paper not only gives a detailed description of synthesis and utilization of MOF@GO composite for CO 2 capture, but also provides a full picture of understanding the adsorption kinetic and adsorption mechanism of MOF and MOF@GO composite, which will give significant guidance to the future work. [ABSTRACT FROM AUTHOR]

• Two biological and seven chemical CO 2 transformation technologies are introduced. • Review of recent progress in experimental and modelling/simulation studies. • Process intensification for CO 2 transformation technologies is included. • Analysis of research trends and CO 2 utilisation projects carried out worldwide. • Challenges facing CO 2 transformation technologies and future prospects summarised. To prevent global warming and climate change caused by CO 2 emissions, the Intergovernmental Panel on Climate Change (IPCC) recommends lowering CO 2 emissions to limit the global temperature to 1.5 °C. In addition to carbon capture and storage (CCS) technologies, there is a growing interest to explore CO 2 utilisation. Several review papers exist in the literature either focusing on one or two CO 2 transformation technologies or covering only experimental studies. This review paper addresses the gap by classifying CO 2 transformation technologies and looking at products from CO 2 conversion. It reviews experiment and modelling/simulation-based studies for CO 2 biological and chemical conversion processes to assess their technical barriers. A detailed analysis of their technology readiness level, cost, market and environmental benefits are also elaborated. Finally, the research trend and projects for CO 2 transformation technologies worldwide as well as the key challenges hindering their commercial deployments are carefully outlined. The analysis of the research trend shows a significant increase in research for CO 2 utilisation with hydrogenation and electrochemical reduction being the most studied technologies since 2016. 53% of the projects are laboratory projects whereas, only 14% account for commercial projects. There is currently no commercial project for plasma catalysis, photochemical, electrochemical and non-photosynthetic technologies. The USA holds the highest number of 45 projects including 8, 6, 10 and 21 commercial, demonstration, pilot and laboratory projects, respectively. The development of improved catalysts and process intensification techniques are highly needed for successful scale-up of CO 2 transformation technologies. [ABSTRACT FROM AUTHOR]

Clathrate hydrates, commonly called gas hydrates, are non-stoichiometric inclusion compounds with tunable gas storage and separation capabilities. Various efforts have been made to apply these hydrates to energy and environmental fields including energy storage and greenhouse gas capture and separation technologies. Although the unary use of gaseous guest molecules such as methane, carbon dioxide, and nitrogen is generally expected to achieve maximal storage capacity by filling the guest in both small and large cages of each structure, introducing additional liquid guest molecules into the clathrate hydrates could be a more feasible option from an engineering perspective, since such liquid guest molecules often play a critical role in stabilization of the clathrate hydrate by shifting the thermodynamic phase equilibria to practically implementable milder pressure and temperature conditions. Here, we focus on the binary neopentyl alcohol clathrate hydrates with gaseous guest molecules, including carbon dioxide, methane, and nitrogen, to provide a better understanding of the complex nature of the host–guest interactions occurring in the clathrate hydrates. Thermodynamic P – T phase equilibria were measured, and spectroscopic analyses were performed employing HRPD, Raman, and NMR spectrometers. The results revealed that the NPA guest molecule forms sI or sII hydrate depending on the binary gaseous guest molecules. This paper also reports for the first time that the composition of CO 2 guest molecules may be ‘tuned’ within the cages of sI hydrate of NPA. [ABSTRACT FROM AUTHOR]

A gliding arc plasma is a potential way to convert CO 2 into CO and O 2 , due to its non-equilibrium character, but little is known about the underlying mechanisms. In this paper, a self-consistent two-dimensional (2D) gliding arc model is developed, with a detailed non-equilibrium CO 2 plasma chemistry, and validated with experiments. Our calculated values of the electron number density in the plasma, the CO 2 conversion and energy efficiency show reasonable agreement with the experiments, indicating that the model can provide a realistic picture of the plasma chemistry. Comparison of the results with classical thermal conversion, as well as other plasma-based technologies for CO 2 conversion reported in literature, demonstrates the non-equilibrium character of the gliding arc, and indicates that the gliding arc is a promising plasma reactor for CO 2 conversion. However, some process modifications should be exploited to further improve its performance. As the model provides a realistic picture of the plasma behaviour, we use it first to investigate the plasma characteristics in a whole gliding arc cycle, which is necessary to understand the underlying mechanisms. Subsequently, we perform a chemical kinetics analysis, to investigate the different pathways for CO 2 loss and formation. Based on the revealed discharge properties and the underlying CO 2 plasma chemistry, the model allows us to propose solutions on how to further improve the CO 2 conversion and energy efficiency by a gliding arc plasma. [ABSTRACT FROM AUTHOR]

In this paper, we report on an experimental study on the influence of low-frequency horizontal vibration of a vertical millimeter-size channel with Taylor bubbles. We investigated the motion, shape and dissolution rate of individual elongated Taylor bubbles of air and CO 2 , which were freely rising in stationary water. Bubble size and dissolution rate were determined from microfocus X-ray radiographs. From the shrinking rate we calculated the liquid-side mass transfer coefficient. The rise velocity of bubbles and surface wave motion were analyzed using a videometric technique. The comparison of the results for the stationary and the oscillating channel showed that mechanical vibration of the channel is able to enhance the mass transfer coefficient from gas to the liquid phase by 80%–186%, depending on the frequency and amplitude of vibration. It was found that channel oscillation causes the increase of free rise velocity of bubbles which is mainly attributed to the development of propelling interfacial waves and increase of liquid film flow rate. Furthermore, analyzing the surface wave motion of bubbles revealed that the enlargement of contact area between the phases and the increased mixing enhances the mass transfer additionally up to 30% compared to non-agitated bubbles of similar Peclet number. [ABSTRACT FROM AUTHOR]

• Bi-functional Mn 2 Co 1 O x /iron mesh (IM) monolithic catalysts was developed. • High NO x and CO conversions (99.7% and 98.2%) were achieved at 160 °C. • Mn 2 Co 1 O x /IM monolithic catalysts presented good water/SO 2 resistance. • The reaction mechanism between NH 3 -SCR and CO oxidation was discussed. NO x and CO are two main pollutants in the coke oven flue gas emissions, and their treatment faces huge challenges. Under oxygen-enriched conditions, CO is rapidly oxidized to CO 2 prior to proceed CO-SCR reaction, therefore, NH 3 -SCR technology incorporated with CO oxidation reaction is a promising approach to remove NO x and CO simultaneously. Considering the practical application, so far, there is no efficient monolithic catalyst capable of removing NO x and CO pollutants simultaneously at low temperatures (160–200 °C). In this paper, Mn 2 Co 1 O x /iron mesh (IM) monolithic catalysts were developed using a hydrothermal method. By tuning the redox properties, surface acidity, and oxygen vacancies, the optimized catalyst exhibits an outstanding catalytic performance (99.7% NO x conversion and 98.2% CO conversion at 160 °C) and excellent water and SO 2 resistance. The synergistic effect and interaction mechanism between NH 3 -SCR and CO oxidation are systematically revealed by correlation characterization and DFT calculations. It was found that Mn 2 Co 1 O x /IM has advantages in adsorbing NH 3 and CO at Mn and Co sites, respectively, which weaken the inhibition of CO oxidation by NH 3. Besides, a strong interaction and charge transfer take place between Fe substrate and the active component which affect the surface-active sites, further improving the activity of Mn 2 Co 1 O x /IM. We believe that this synthesis of efficient integrated catalysts has potential application prospects in coke oven flue gas treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Indirect Z-type multiple Bi/BiO 2-X –Bi 2 O 2 CO 3 /BiOCl@Bi–MOF heterojunction was prepared. • Composite show high photocatalytic activity for antibiotics in actual water matrices. • Boosted activity is due to synergistic effect between multiple active components. • Retention of MOF structure in multiple composite provides more active sites. • Indirect Z-type heterojunction boost MOF's light utilization and e–-h+ separation. Currently, the chemical properties of metal–organic frameworks (MOFs) can be fully exploited by combining inorganic semiconductors with MOFs to improve their narrow light absorption range and high carrier separation efficiency. Therefore, in this paper, indirect Z-type multicomponent Bi/BiO 2-X –Bi 2 O 2 CO 3 /BiOCl@Bi–MOF heterojunction with plasma Bi and BiO 2-X –Bi 2 O 2 CO 3 co-modified with BiOCl@Bi–MOF were successfully prepared through combining hydrothermal and photodeposition methods using BiOCl@Bi–MOF composites as active carriers. The ability to remove chlortetracycline (CTC) with Bi/BiO 2-X –Bi 2 O 2 CO 3 /BiOCl@Bi–MOF was investigated by modulating the factors, such as photodeposition time, presence or absence of MOF structure, different water source, and different inorganic salts. In the CTC degradation experiments, the optimized Bi/BiO 2-X –Bi 2 O 2 CO 3 /BiOCl@Bi–MOF-10-0.3 composite showed the best photocatalytic degradation efficiency (94.6%) within 90 min of full-spectrum light illumination. Its corresponding first-order kinetic rate constant (0.0315 min−1) was 2.5 and 1.6 times higher than those of MOF-free structural composites Bi/BiO 2-X –Bi 2 O 2 CO 3 /BiOCl-10-0.3 and BiOCl@Bi–MOF, respectively. The increased photocatalytic activity is attributed to the synergistic effect between the MOF structure, metal Bi, BiO 2-X –Bi 2 O 2 CO 3 , and BiOCl@Bi–MOF carrier. By combining the results of active species capture experiments, electron spin resonance techniques (EPR), and photoelectrochemical experiments, we have deduced a possible indirect Z-type heterojunction photocatalytic mechanism between Bi, BiO 2-X –Bi 2 O 2 CO 3 and BiOCl@Bi–MOF. The possible photocatalytic degradation pathways and products of CTC were deduced by combining liquid chromatography-mass spectrometry (LC-MS). This work supplies valuable guidance for preparing metal nanoparticles/semiconductor/MOFs with an indirect Z-type heterojunction photocatalyst for the repair of natural CTC wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • The activity of electrochemical CO 2 RR is boosted by modulating the electronic structure of Au. • Metal-support interaction (MSI) combined with CeO 2 and MWCNT activates Au. • Matched work function using CeO 2 and MWCNT modifies the electronic structure of Au. • MSI via heterostructure could increased the binding strength of CO 2 adsorption verified by CO 2 -TPD. • Au/CeO 2 /MWCNT exhibits excellent electrocatalytic performance for CO 2 RR. Electrochemical CO 2 reduction reaction (CO 2 RR) is a promising method to convert CO 2 into high value carbon products. For commercial applications, the energy efficiency of CO 2 RR needs enhancement. Designing superior electrocatalysts is important to increase energy efficiency. This paper reports that the catalytic properties of Au can be enhanced by metal-support interaction (MSI) through CeO 2 and a multi-walled carbon nanotube (MWCNT). A heterostructure for MSI is constructed by matching work function using CeO 2 and MWCNT to modify the electronic structure of Au via cascade electron transfer. Through MSI, the Au/CeO 2 /MWCNT heterostructure exhibits 4.2 times higher CO selectivity than Au/CB, and 1.6 times higher CO selectivity than Au/CeO 2 at 200 mA cm−2. As a result, the energy efficiency of CO production from CO 2 RR can be significantly increased using Au/CeO 2 /MWCNT. These findings show the importance of MSI in designing high-performance catalysts for CO 2 RR. [ABSTRACT FROM AUTHOR]

• Bimetallic nitride heterostructures is constructed to broaden the optical response. • The C@VN/TiN sample are synthesized by ammonia-assisted one-step calcination. • The C@VN/TiN sample has the best photoreduction CO 2 performance. There are still many challenges in inhibiting the recombination and differentiation of photogenerated carriers from promoting the conversion of CO 2 into hydrocarbons. Based on the functional differentiation of different metal sites, bimetallic nitride heterostructures is constructed to broaden the optical response and promote the separation of charge carriers in this work. Herein, carbon substrate-loaded double nitride heterostructure composites C@VN/TiN are synthesized by ammonia-assisted one-step calcination. In all samples, the C@VN/TiN-3 sample has the best photoreduction CO 2 performance with the promotion of lactic acid (LA) reagent. And the CH 4 yield of the C@VN/TiN-3 sample is 775 μmol g−1 h-1, which is 7.6 times and 10.3 times higher than C@VN (102 μmol g−1 h-1) and C@TiN (75 μmolg−1 h-1), respectively. The generation, separation, and migration of photogenerated electron-hole pairs are studied kinetically through transient photocurrent responses, electrochemical impedance spectroscopy and photoluminescence spectroscopy. The position and process of adsorption and activation of CO 2 and H 2 O are deduced by in situ characterization and reaction potential, and the determined possible path is explored by the peak of intermediates. This paper reveals the important roles of co-catalytic agents, ohmic junctions, and the function of bimetallic actives in enhancing photocatalytic activity, providing new ideas for constructing efficient photocatalysts. [ABSTRACT FROM AUTHOR]