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Recently, photo switching porous materials have been widely reported for low energy costed CO2 capture and release via simply remoted light controlling method. However, most reported photo responsive CO2 adsorbents relied on metal organic framework (MOFs) functionalisation with photochromic moieties, and MOF adsorbents still suffered from chemically and thermally unstable issues. Thus, further metal free and highly stable organic photoresponsive adsorbents are necessary to be developed. CTFs, because of their high porosity and stability, have attracted great attention for CO2 capture. Considering the high CO2 uptake capacity and structural tunability of CTFs, it suggests high potential to fabricate the photoswitching CTF materials by the same functionalisation method as MOFs. Herein, the first series of photo switching CTFs were developed for low energy CO2 capture and release. Apart from that, the CO2 switching efficiency could be doubled either through the azobenzene numbers adjusting method or through the previously reported structural alleviation strategy. Furthermore, the pore size distribution of azobenzene functionalised PCTFs also could be tuned under UV exposure, which may contribute to the UV light induced decrease of CO2 uptake capacity. These photoswitching CTFs represented a new kind of porous polymers for low energy costed CO2 capture. [ABSTRACT FROM AUTHOR]

Direct air capture (DAC) of CO 2 is considered one of the most promising carbon capture methods to reduce ambient CO 2 concentration for climate change mitigation. Biochar represents an attractive adsorbent for DAC because it is environmentally friendly and cost-effective. In this work, KOH-activated bamboo biochar shows the CO 2 capture capacity of 3.49 mmol g−1 (25 °C, 1 bar), and it is used as an adsorbent to perform direct air capture using a fixed-bed reactor with an ambient CO 2 capture capacity of up to 51.74 μmol g−1. Furthermore, the effect of relative humidity on CO 2 adsorption by biochar was investigated and exhibited promising stability under 2.7% relative humidity. However, the biochar activity for CO 2 capture is reduced to 63.88% under 67.1% humidity after 50 cycles. [Display omitted] • KOH was used to activate bamboo-derived biochar. • Bamboo biochar was investigated in direct air capture of CO 2. • Gas selectivity of biochar during direct air capture. • Effect of relative humidity on direct air capture efficiency. [ABSTRACT FROM AUTHOR]

Carbon capture and sequestration technologies are essential to reduce CO 2 emissions which are responsible for global warming. Carbon-based materials can play an important role in the reduction of CO 2 emissions. These materials are normally produced from biomass through technologies such as pyrolysis and hydrothermal carbonization. The type of biomass feedstock and biomass conversion conditions can significantly affect the textual properties and surface chemistry of the carbon materials. Various modification methods such as material activation or N-doping can improve the properties of carbon materials to obtain better CO 2 capture effects. This review summarizes recently reported research in the areas of using biomass-based materials for CO 2 capture. The technologies of biomass conversion to carbon materials and modification of the carbon materials are critically analyzed. Meanwhile, the mechanisms of the CO 2 capture process and research of different modification carbon materials for CO 2 capture are also discussed. Finally, potential future research directions are suggested to promote carbon capture using biomass-based materials. • The preparation technologies of carbon materials and influencing factors are discussed. • Traditional and emerging carbon material modification methods are summarized. • Recent researches of carbon materials for CO 2 capture and its capture mechanisms are discussed. • Future research directions and challenges in carbon materials for CO 2 capture are discussed. [ABSTRACT FROM AUTHOR]

Anaerobic digestion of agricultural waste for producing biogas as a renewable energy source is an established and promising technological option, producing a huge quantity of solid digestate as residue waste. Valorization of solid digestate into high-value products is necessary to make the anaerobic digestion process more cost-effective and enhance environmental benefits. In this study, activated carbon was fabricated from solid digestate with phosphoric acid activation in the fixed bed reactor. The physicochemical properties of the activated carbons have been analyzed by elemental analysis, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and N 2 adsorption and desorption isotherms. The effect of H 3 PO 4 /digestate char impregnation ratio on structural and morphological change of the produced activated carbon was tested, and the function of H 3 PO 4 in the activation procedure was discussed. The results indicated that an appropriate H 3 PO 4 /digestate char ratio was useful for the creation of pore structure. The highest surface area of 201 m2/g was attained at H 3 PO 4 /char ratio of 2 and at 600 °C. The potential for the use of the prepared activated carbon for CO 2 capture was also evaluated thermogravimetrically under dynamic conditions, indicating good cyclic stability. This study provides the feasibility of integrating anaerobic digestion for biogas with subsequent activated carbon production from solid digestate. • H 3 PO 4 /digestate impregnation ratio greatly affected textural and surface property of activated carbons. • The SiO 2 in digestate char could react with P to form silicon diphosphate during H 3 PO 4 activation. • Digestate-derived activated carbon has a good CO 2 capture cyclic stability. [ABSTRACT FROM AUTHOR]

Engineered biochar derived from wood waste pyrolysis in molten salts were developed for effective CO 2 /N 2 separation. The production conditions were customized to obtain the biochar with high CO 2 capture capacity and CO 2 /N 2 selectivity by tuning the type of molten salts (MgCl 2 -KCl, ZnCl 2 -KCl, ZnCl 2 -NaCl-KCl, and K 2 CO 3 -Na 2 CO 3 -Li 2 CO 3), salt/feedstock ratios (1:1 and 3:1) and pyrolysis temperatures (600 and 800 °C). High temperature (800 °C) and moderate salt loading (salt/feedstock ratio of 1:1) benefited the CO 2 adsorption by providing an increased surface area and highly dispersed metal species as adsorption sites. PSL-3-800 and PSL-3-600 (K 2 CO 3 -Na 2 CO 3 -Li 2 CO 3 biochar) showed the highest CO 2 capacity (4.5 mmol g−1, 0 °C, 100 kPa) and the highest CO 2 /N 2 selectivity (28.5), respectively, among the engineered biochar developed in this study. In addition, ZP-3-600 showed the highest selection parameter (S) in both PSA and VSA processes, indicating the promising CO 2 capture performance under PSA/VSA conditions. A high recovery rate (89%) of molten salts was achieved. These results suggest a new pathway for upcycling biowaste as eco-friendly and effective adsorbents for gas adsorption and separation. [Display omitted] • Molten salt-assisted biochars were prepared for CO 2 capture from N 2. • K 2 CO 3 -Na 2 CO 3 -Li 2 CO 3 engineered biochar showed the highest CO 2 capacity. • A high pyrolysis temperature (800 °C) facilitated the formation of large surface area. • Separation potential was evaluated under pressure/vacuum swing adsorption conditions. • Recovery rate of soluble molten salt in the biochar was up to 89%. [ABSTRACT FROM AUTHOR]

• Calcium looping and chemical looping are isothermally integrated for CO 2 capture and CO generation. • Ni promoted Fe-CaO achieves effective and stable cyclic calcium chemical dual looping. • Ni promoted Ca 2 Fe 2 O 5 plays as the oxygen carrier to achieve the in-situ chemical looping. • Ca 2 Fe 2 O 5 improves the calcium looping stability by acting as a thermally stable physical barrier. • Steam or air purge after hydrogenation is effective to avoid CO generation in carbonation. Reverse water–gas shift reaction using renewable H 2 is a promising route for CO 2 upgrade, however, it is restricted by the equilibrium. The chemical looping reverse water–gas shift reaction using oxygen carriers (i.e. Fe) has proven a more effective CO 2 utilization process to produce CO. However, CO 2 with high purity is needed to obtain concentrated CO. Herein, we propose a calcium chemical dual looping using one-pot sol–gel synthesized Ca-Fe dual functional materials (DFMs). The CO 2 in the exhaust gas (∼10% CO 2) can be captured and transformed into carbonates and then in-situ converted into CO through continuous chemical looping in H 2 atmosphere. This process avoids CO 2 enrichment, storage and transportation and simultaneously realizes efficient CO 2 conversion. The Ca-Fe DFMs possessed significantly improved catalytic efficiency (enhanced real-time CO generation rate) compared to CaO. It is found that Ni 1 Fe 9 -CaO could optimally achieve 11.3 mmol g DFM −1 CO yield, 82.5% CO 2 conversion and 99.9% CO selectivity at 650 °C. Notably, Ni 1 Fe 9 -CaO displayed high CO 2 conversion (>80%) and CO selectivity (>99.9%) during the cycle tests and possessed enhanced stability in relation to CO yield after 10 cycles (20.9% and 35.5% decrease for Ni 1 Fe 9 -CaO and CaO, respectively). Herein, Ca 2 Fe 2 O 5 plays two roles: acting as an oxygen carrier for in-situ chemical looping to produce CO and a thermally stable physical barrier to retard the sintering of CaO. It is noted that Fe-related species could be reduced into the metallic state at the end of hydrogenation, resulting in CO formation in the following CO 2 capture process. [ABSTRACT FROM AUTHOR]

The emerging integrated CO 2 capture and utilization (ICCU) potentially contributes to net zero emissions with low cost and high efficiency. The catalytic performance in ICCU process is highly restricted by the equilibriums of carbonate decomposition and dry reforming of methane (DRM). Here, we engineer a unique yolk-shell dual functional nanoreactor construction to improve the catalytic performance via confined catalysis. By tailoring the carbonates decomposition kinetics and confining the CO 2 diffusion path, ∼92% CO 2 conversion is achieved over (Ni/Ca)@Si and shows no distinct activity loss in 10 cycles at 650 °C. The formed Ca 2 SiO 4 shells restrain the sintering of CaO yolks by acting as physical barriers, and stabilize the Ni particle size. It is also confirmed on in situ DRIFTS that the integrated DRM might occur via carbonyls, formates and CHO intermediates, in which formates species are highly dependent on Ni-carbonates interfaces. [Display omitted] • Ni-functionalized Ca@Si yolk-shell nanoreactors achieves effective CO 2 capture and in situ methane dry reforming. • Yolk-shell structure promote the catalytic performance by confined catalysis. • Ca 2 SiO 4 shell stabilizes both the CaO yolk and catalytic sites. • Formates are dependent on Ni-carbonates interfaces. [ABSTRACT FROM AUTHOR]

• Ni/SiO 2 activation and CO 2 supply are pivotal for ICCU-DRM. • Reverse Boudouard reaction plays an essential role in CO 2 conversion. • Ni/SiO 2 -CaO interaction needs to be optimised to enhance ICCU-DRM efficiency. • Synergies exist between Ni/SiO 2 catalyst and CaO sorbent in CO 2 conversion. Integrated carbon capture and utilisation (ICCU) is an emerging technology for simultaneous CO 2 adsorption and conversion into value-added products. This provides a more sustainable approach compared to carbon capture and storage. Dual-functional materials (DFMs) that couple CO 2 sorbents (e.g. CaO) and catalysts (e.g. Ni) enable direct utilisation of sorbed CO 2 for reactions like dry reforming of methane (DRM). However, the potential interactions between sorbent and catalyst components within DFMs may induce distinct mechanisms compared to individual materials. Elucidating these synergies and interfacial phenomena is vital for guiding the rational design of DFMs. This article investigates the respective roles of Ni/SiO 2 catalyst and sol–gel synthesised CaO sorbent in integrated CO 2 capture and utilisation via dry reforming of methane (ICCU-DRM) using a decoupling approach. Through decoupled reactor experiments, it is found that Ni/SiO 2 activates CO 2 to react with carbon deposits from CH 4 decomposition, achieving maximal CO and H 2 yields of 43.41 mmol g−1 and 46.78 mmol g−1 as well as 87.2 % CO 2 conversion at 650 °C. Characterisation shows that coke would encapsulate Ni nanoparticles and be active for CO 2 conversion via Boudouard reaction, indicating sufficient catalyst-sorbent contact is necessary for CO 2 spillover. In-situ DRIFTS reveals that no obvious CH 4 -CaCO 3 reaction occurs, CO 2 chemisorption on Ni/SiO 2 enables the reverse Boudouard reaction, which is further verified by DFT calculations. The findings elucidate the dependent and synergistic roles of Ni/SiO 2 and CaO/CaCO 3 in ICCU-DRM, and highlight the importance of catalyst-adsorbent interactions in optimising dual-functional materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • The presence of acidic sites can accelerate the hydrogenation of carbonate. • ZrO 2 reduce the formation barrier of intermediates in carbonate hydrogenations. • ZrO 2 doped Ni/CaO can quickly complete hydro-methanation of carbonate in ICCU. • Steam reduces the hydrogenation rate of carbonate and improve CO 2 capture capacity. Carbonate hydrogenation is a new path for the conversion of metal carbonate with potentially lower energy consumption and CO 2 emissions comparing to the traditional thermal decomposition, and the integrated CO 2 capture and utilization (ICCU) represents its latest development. However, the slow hydrogenation rate of carbonate at low temperatures is one key scientific challenge for applications. Herein, we report an acidity regulation approach to prepare ZrO 2 -doped Ni/CaO dual-function material with good CO 2 capacity, fast and highly selective conversion below 600 °C for integrated CO 2 capture and utilization by methanation (ICCU-methanation). Experiments and DFT calculations show that the introduction of ZrO 2 as acid sites effectively strengthens *H adsorption and reduces the formation barrier of intermediate *COOH during carbonate hydrogenation. Thus, Ni 10 (ZrO 2) 10 CaO 80 exhibits a CH 4 STY of 14.1 mmol∙min−1∙g Ni −1 at 550 °C, 6 times higher than the reference DFM. Furthermore, the presence of O 2 in flue gas is observed to have no effect on ICCU-methanation, but steam could delay the in-situ methanation. Long-term cyclic test shows that the optimal Ni 10 (ZrO 2) 5 CaO 85 has a stable CO 2 capacity of 7.5 mmol ∙g DFM −1, 98 % CO 2 conversion and 95.5 % CH 4 selectivity under flue gas containing both steam and O 2 at 600 °C, suggesting a good potential to be applied in ICCU-methanation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simple and low-cost marble was used for integrated carbon capture and utilisation. • The effect of O 2 and H 2 O in flue gas on the performance of marble was studied. • The highest CO 2 capture capacity of 11.3 mmol g−1 was reported. • The highest CO yield 9.2 mmol.g−1 and 100 % selectivity was reported. • The mechanism for excellent cyclic stability and degradation of marble was proposed. Marble dust is a low-cost, robust, and environmentally friendly natural material for integrated carbon capture and utilization (ICCU). This study demonstrates the effect of oxygen and water in the flue gas on the ICCU performance of marble dust when it is integrated with reverse water gas shift reaction (RWGS), which could potentially be scaled up for the application of marble dust. The inclusion of water vapor in flue gas augmented the capture ability of calcined marble (CM) to eliminate 12.8 mmol g−1 CO 2 from flue gas and achieved the highest CO yield of 10.2 mmol g−1 with almost 100 % CO selectivity. The introduction of O 2 , despite lowering CO 2 capture efficiency, retained the pore structure of CM, boosting a lasting CO producing. With inert MgO as a stabilizer in CM, the segregation between two-layered CaO and MgO crystalline structure alleviated the sintering and carbon deposition, enhanced diffusion and retained superior structural stability over consecutive cycles than raw CaO. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultra-low CO 2 emissions were achieved in biomass gasification using air. • Cost-effective waste marble powder and gasification agent (air) were employed. • Marble shows superior performance in resisting carbon deposition, only 7.45 wt%. Addressing the high CO 2 emissions from biomass gasification is crucial for enhancing the sustainability and environmental profile of this technology. This work proposes a novel approach by integrating the biomass gasification process with carbon capture and utilisation (IGCCU), to tackle the substantial challenge of traditional biomass gasification, which leads to high CO 2 emissions. Specifically, during the biomass gasification stage, this novel approach successfully captured 14.39 mmol g−1 lignin of CO 2 , based on benchmark conditions. The captured CO 2 is subsequently converted into CO during the hydrogenation stage, achieving a peak CO concentration of 1.58 %. The results reveal that maintaining a marble feeding mass of 6 g and setting the reaction temperatures for gasification, carbon capture, and hydrogenation at 500 °C, 400 °C, and 550 °C, respectively, consistently ensures ultra-low CO 2 emissions throughout the entire process. "Ultra-low CO 2 emissions" specifically refers to the absence of CO 2 signals throughout the entirety of the IGCCU process, encompassing stages such as biomass gasification, CO 2 capture, and CO 2 conversion. Notably, CO 2 conversion and CO selectivity remain at a stable 100 % level over 8 cycles as only CO was generated during the hydrogenation stage, underscoring the excellent stability of this novel technology. Furthermore, the utilisation of low-cost sorbent material (waste marble powder) and the readily available biomass gasification agent (air) enhance the economic feasibility of this new technology while demonstrating robust resistance to carbon deposition. [ABSTRACT FROM AUTHOR]

Under the high attention of the international community to CO 2 emissions, the capture utilization and storage (CCUS) and the CO 2 hydrogenation fuel production have become two popular directions, especially for the combination of the two processes. In this paper, the production of liquid fuels via the methanol synthesis pathway in an integrated CCUS system based on Aspen Plus models was studied. The NH 3 -CO 2 -H 2 O absorption was used to capture CO 2 and hydrogen was provided by water electrolysis using renewable energy sources. A two-stage reactor with a recirculating stream was specified for the process of CO 2 hydrogenation to synthesize methanol, and the liquid fuel dimethyl ether (DME) was reproduced by dehydrating methanol (Power-to-Liquid). The amount of absorbent used for the carbon capture process was determined and the yield differences due to the number of cycles in the intermediate methanol synthesis reaction were analyzed. It is possible to convert 4.15 t of CO 2 per tonne of DME produced at the mass material balance of the process. The optimization of the heat exchange network and the energy requirements for the total process were evaluated. It is calculated that the energy involved in producing 1 ton of DME in the process model is 176 GJ. The analysis of the overall process and the evaluation of models could provide options for the possibility of CCUS engineering application. [Display omitted] • An integral process model converts CO 2 to liquid fuels by methanol synthesis. • Treatment options are proposed for emissions that accumulate in the cycle of the process. • The model offers energy requirement assessment for possible engineering applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni 0.05 /CaO 0.95 were evaluated for integrated CO 2 capture and utilization. • NiO needs to be reduced by CH 4 after the CO 2 capture stage to initiate the DRM reaction. • O 2 and moisture triggered Ni and CaO expansion inhibiting NiO reduction and decreasing DFM performance. Global warming and climate change require urgent reduction of CO 2 emissions. Integrated carbon capture and utilisation combined with dry reforming of methane (ICCU-DRM) has the potential to mitigate greenhouse gas emissions by capturing and converting CO 2 and CH 4 into valuable syngas. However, the performance and stability of dual-functional materials (DFMs) are unclear under real-world flue gas conditions, particularly in the presence of steam and O 2. In this study, we elucidated the mechanisms of the performance of a Ni 0.05 /CaO 0.95 DFM under various flue gas conditions and investigated the combined effects of steam and O 2 on CO 2 uptake, CO and H 2 yields and cyclic stability. Our approach includes the synthesis and evaluation of the DFM using advanced characterisation techniques, such as XRD, in-situ infrared spectroscopy, CH 4 -TPR, SEM, EXD, FIB-SEM, BET, and XPS, to gain insights into the properties and behaviour of the DFM under different flue gas conditions. The findings show that under the simulated flue gas condition (10.0 % CO 2 + 6.0 % H 2 O + 6.7 % O 2 /N 2), there was a significant deterioration in performance, with CO 2 uptake of only 5.7 mmol.g-1, average H 2 yield of 11 mmol.g−1 and average CO yield of 6.2 mmol.g−1. While under the ideal condition (10.0 % CO 2 /N 2), the CO 2 uptake, average H 2 yield and average CO yield were 10.7 mmol.g−1, 16.9 mmol.g−1 and 23.1 mmol.g−1, respectively. FIB-SEM and XPS analysis highlighted the combined effect of steam and O 2 on the performance of Ni 0.05 /CaO 0.95 DFM during ICCU-DRM. Notably, the presence of O 2 promoted the oxidation of Ni, resulting in decreased catalytic activity and volumetric expansion of Ni particles. Furthermore, the presence of steam promoted CO 2 adsorption, inducing additional volumetric expansion of the CaO component of DFM. These synergistic expansions form a dense shell on the surface, hindering the reduction of internal NiO, thereby diminishing DFM performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biomass gasification was integrated with CO 2 capture and utilization technology. • 100% CO 2 capture and 100% CO 2 conversion were achieved through IGCCU technology. • High-value syngas (CO and H 2) was produced while achieving a CO 2 net zero process. • 0.95 mmol g−1 CaO g−1 lignin of CO was generated during the CO 2 conversion process. Biomass energy plays a crucial role in mitigating carbon emissions. However, the existing gasification technology faces challenges such as releasing undesirable CO 2 in the produced syngas. Here we propose a new concept for achieving zero CO 2 emissions by integrating gasification with CO 2 capture and utilization (IGCCU) for the first time. During lignin gasification, valuable syngas (H 2 /CO) can be produced, and CO 2 in the gaseous products can be simultaneously captured by CaO. After completing the lignin gasification process, the captured CO 2 can be effectively converted to CO by switching the carrier gas from N 2 to H 2. The results show that the entire process achieves zero CO 2 emissions with carbonation and hydrogenation process at 400 °C and 550 °C, respectively. This approach allows a significant reduction in CO 2 yield from 0.95 mmol g−1 CaO g−1 lignin (benchmark experiment) to nearly 0, using CaO as an adsorbent and catalyst. The disappeared CO 2 was converted into 0.95 mmol g−1 CaO g−1 lignin of CO, by introducing H 2 to the sorbent regeneration stage. Furthermore, excellent cyclic stability has been achieved with zero CO 2 emissions after five cycles and consistent 100% CO 2 conversion during the CO 2 utilization stage. [ABSTRACT FROM AUTHOR]

CCUS technology is an important means to achieve carbon neutralization of energy utilization, in which the ammonia CO 2 -capture method is a relatively mature technology, with some problems (such as low CO 2 absorption efficiency and serious ammonia escape). An ethanol/biochar synergistic ammonia carbon capture technology is proposed, and the mass transfer coefficient is studied by wetted-wall column, so as to assist in proving that biochar and ethanol have synergistic effect on the absorption of CO 2 by ammonia. The simulation shows that the micropores in biochar adsorb and enrich CO 2 , the mesopores and macropores diffuse and transport CO 2 , and dynamically retain free NH 3 , thereby enhancing the mass transfer capacity of CO 2 in the carbon capture system. And the experiment shows that the mass transfer efficiency of biochar-ethanol to the reaction solution is increased by 15.4%, which is higher than that of ethanol (7.1%),but biochar can make ammonia escape seriously. If the ammonia concentration can be maintained constant, the enhancement effect of the pore structure of biochar on the diffusion of CO 2 into ammonia will provide a new direction for the improvement of CO 2 capture by ammonia method. [Display omitted] • Solid-liquid two-phase functional crosslinking enhanced ammonia CO 2 capture. • Biochar promotes the ammonia absorption of CO 2 in the early stage. • As the reaction progresses, biochar inhibits the ammonia absorption of CO 2. [ABSTRACT FROM AUTHOR]

Digestate solid is a waste produced by biogas plants. It has a promising potential for the application of direct capture of CO 2 from the air. In this study, digestate soild was carbonised under different temperatures to obtain digestate char. The carbon capture performance using the produced digestate char was further explored. Firstly, the structural properties of the prepared digestate char were characterised by N 2 -adsorption/desorption, X-ray diffractometry (XRD), Raman, X-ray photoelectron spectroscopy (XPS) and ultimate analysis. It was revealed that the addition of the carbonisation temperature from 400 to 800 °C led to the increase of specific surface area and total pore volume. When the carbonisation temperature increased, the degree of the molecular cleavage increased, and the content of graphite-C (C–C) increased, while the digestate char formed more carbonyl (C O), phenol, alcohol, or ether group (C–O). Furthermore, the effects of carbonisation temperature, gas flow rate and the adsorption temperature on the carbon capture performance of the digestate char were evaluated. The results showed that the carbon capture ability increased with the increase of carbonisation temperature, and with the increase of gas flow rate, the capacity of CO 2 capture first increased and then decreased. In addition, when the adsorption temperature increased, the capacity of CO 2 capture further decreased. • The structural changes of digestate char with pyrolysis temperatures were systematically studied. • Digestate char shows good CO 2 capture performance during direct air capture. • CO 2 capture ability of digestate char is affected by carbonisation temperature, adsorption temperature and gas flow rate. [ABSTRACT FROM AUTHOR]

Graphical abstract An efficient Ce-promoted one-pot synthesized multifunctional catalytic material for integrated carbon capture and conversion to CO is reported with high stability and CO 2 conversion. Highlights • Dual functional Ni-Ca materials are developed with the promotion of Ce. • Simultaneous sorbent regeneration and CO production is demonstrated. • Catalyst with a Ca/Ni/Ce molar ratio of 1:0.1:0.033 displays almost 100% CO selectivity and 51.8% CO 2 conversion. • 20 stable cycles of integrated CO 2 capture and conversion is obtained. Abstract Excessive anthropogenic CO 2 emission in the atmosphere is considered as one of the main contributions to the serious climate changes. However, with the growth of global economics, more fossil fuels will be consumed to feed the global activity, especially in developing countries. Thus, CO 2 needs to be captured for storage or converted to fuels or value-added chemicals. Herein, we propose and demonstrate a one-pot method synthesized dual functional materials (DFMs), which contain a sorbent coupled with a catalyst component, allowing the sorbent regeneration and CO 2 conversion to CO are performed simultaneously in a single reactor. This process requires no additional thermal energy for the regeneration of sorbents. In addition, CeO 2 is incorporated into the DFMs to largely enhance the stability of the materials for the process, and the influence of different Ce loadings on the performance of integrated CO 2 capture and conversion is studied. It is found that the DFMs with a Ca/Ni/Ce molar ratio of 1:0.1:0.033 displays almost 100% CO selectivity and 51.8% CO 2 conversion in the reverse water-gas shift (RWGS) reaction and a remarkable cyclic stability after 20 cycles of integrated CO 2 capture and conversion. Therefore, the incorporation of Ce into DFMs has two profits, for one thing, the oxygen vacancies generated by CeO 2 directly reduces the dissociated CO 2 regenerated from the DFMs, demonstrating the high CO yield; for another, the well-dispersed CeO 2 , which could act as a physical barrier, effectively prevents the growth and agglomeration of CaO crystallite and NiO species. [ABSTRACT FROM AUTHOR]

• CO 2 in flue gas could be captured and utilised via integrated DRM. • Ni-Ca interactions limitedly contribute due to poor reducibility and accessibility. • Ni 10 -CaO exhibits optimal CO 2 capture and DRM performance. • Optimal Ni loading provides sufficient surface Ni and limited sintering. • Ni particle size does not affect the ICCU performance. Reducing carbon emissions remains a formidable challenge under present energy demands and structures. Integrated CO 2 capture and utilisation (ICCU) provides a promising pathway for directly capturing and simultaneously utilising CO 2 from the diluted exhaust gas. Dry reforming of methane (DRM) can be integrated into the step of catalytic conversion of the captured CO 2 with the advantages of utilising two greenhouse gases to yield valuable syngas (CO + H 2). The process has great challenges of materials development for efficient performance, in particular under realistic conditions such as the presence of O 2 and H 2 O in the flue gas. This work investigated the ICCU-DRM using simulated flue gases (10 % CO 2 + 6.7 % O 2 + 6.0 % H 2 O) in the presence of Ni-CaO dual functional materials, aiming to optimise Ni loading and metal support interaction. It is found that Ni would significantly sinter and further affect the morphologies of CaO adsorbents, resulting in poorer CO 2 capture performances. More notably, the Ni was firstly oxidised during CO 2 capture and subsequently went through a pre-reduction period in the DRM step. Increased Ni loading decreased the difficulty of activation; however, it derived in more severe carbon deposition. To avert the direct contact of carbon deposition and flue gas, extra carbon steam gasification was introduced, and higher Ni loading contributed to selectively yielding syngas as a by-product. The Ni 10 -CaO DFM optimally performed <150 s pre-reduction delay, ∼85 % CO 2 conversion and ∼2 H 2 :CO ratio in the DRM step and ∼75 % CO selectivity in the CSG step at 650 °C. The interaction between Ni and CaO poorly contributes to the performance due to the poor reducibility and accessibility, and the Ni particle size effects only play as spectators in this integrated process. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preparation of biochar graded pore structure by KOH secondary activation. • Biochar promotes the mass transfer process of new ammonia-based CO 2 capture. • Hierarchical biochar provides gas physical adsorption and containment space. • Ult-micropores are good for CO 2 adsorption and mesopores are good for CO 2 diffusion. • Biochar is beneficial to the adsorption-enrichment of CO 2 and the fixation of NH 3. Ammonia-based CO 2 capture technology has crucial impacts on power plants carbon emission reduction, which has become one of the most concerning issues. However, there are limitations faced by traditional capture technology in the absorption rate, ammonia escape and regeneration energy consumption. The functionalized biochar (with a specific surface area of up to 2835.36 m2/g, micropores volume of 77.4 %) was used to enhance the mass transfer process of new ammonia-based (ammonia-ethanol mixed absorbent) CO 2 capture by the bubbling absorption experiment system, combined with Monte Carlo simulations, which explored the adsorption and release characteristics of CO 2 /NH 3 molecules in biochar with different pore sizes. The results show that the CO 2 absorption flux added biochar RH-900 is 59.67 L·min, increased by 16.16 % compared with pure absorbent. And the volume mass transfer coefficient is 1.226 × 10-4mol/m2·s·Pa, increased by 15.3 % compared with the SiO 2. The addition of RH-900 also promotes the CO 2 load capacity of the carbonated solution up to 0.5255 mol/L, enhancing the CO 2 absorption capacity and CO 2 capture efficiency significantly. The ultra-micropores adsorb CO 2 , while the surface of larger pores distributes and achieves the adequate fixation of NH 3. Besides, the mesopores and macropores provide space where the CO 2 is transported and diffused, and the free ammonia concentration is maintained. The study provides an innovative thought for improving the ammonia-based CO 2 capture method and significantly reducing of harmful carbon emissions by biomass energy-carbon capture and storage (BECCS) technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three Ca-MOFs with specific structures were employed as precursors to obtain nano CaO through a two-step thermal transition process. • LAC MOF-derived CaO spheres with an average size of 100 nm achieved a fast adsorption capacity of 11.8 mmol g−1 after 4 cycles. • The structure transition from LAC MOF to CaO spheres was deeply investigated. Calcium looping is considered to be one of the best approaches for industrial CO 2 high-temperature capture, whereas current CaO-based sorbent suffers poor cyclic performance, especially the relations between precursor structure and CO 2 fast adsorption capacity still need to be further revealed. In this work, three calcium-based metal frameworks (Ca-MOFs) with specific structures were employed as precursors to obtain nano CaO through a two-step thermal transition process. It was found that LAC MOF-derived CaO achieved a fast adsorption capacity of 11.8 mmol g−1 (78 % of total adsorption) after 4 cycles. This was because the fiber bundle-like original LAC MOF structure changed gradually to nanosheets after 600 °C pyrolysis and finally formed regular CaO spheres with an average size of 100 nm after an 800 °C -calcination, thereby preventing further aggregation of CaO particles during the thermal transition process. In addition, the adsorption performance did not rely on pore structure, and thus pore-blocking showed little influence on the performance of CO 2 capture. Hence, high stability can be achieved simply by avoiding particle sintering. The systematic study marks the significance of precise tailoring of nano-CaO for achieving the desired performance of CO 2 fast adsorption. [ABSTRACT FROM AUTHOR]

• CO 2 from flue gas could be directly utilised via ICCU-DRM process. • The H 2 O promotes CO 2 capture kinetics, the O 2 throughly oxidises Ni into NiO. • The NiO reduction is not instant and further deteriorated by CaCO 3 coverage. • Carbon deposition contributes to CO, CH 4 and H 2 generation during CO 2 capture. • Introducing steam to consume carbon maintains the harmless CO 2 capture. Integrated CO 2 capture and utilisation via dry reforming of methane (ICCU-DRM) represents a promising and profitable route for directly capturing and converting CO 2 from various CO 2 sources. However, the influence of realistic flue gas conditions on ICCU-DRM remains unknown and challenging. Herein, we investigated the influence of the presence of H 2 O and O 2 in power plant flue gas on integrated CO 2 capture and DRM using Ni 10 -CaO dual functional material (DFM). It is found that H 2 O promoted the kinetics of CO 2 capture, while the O 2 oxidised Ni into NiO and prohibited the performance of utilisation of the captured CO 2 during DRM. Specifically, the delay of pre-reduction of NiO and the coverage of catalytic sites by the formed CaCO 3 decreased the process performance and efficiency. The reduction of NiO would instantly generate CO 2 and hinder the contact between CH 4 and Ni, resulting in a lower initial catalytic performance during the CO 2 utilisation (DRM) of ICCU. Due to the occurrence of CH 4 decomposition in DRM, the following CO 2 capture step would produce CO in the flue gas, which could be problematic, owing to the carbon gasification reactions. An extra step of carbon steam gasification (CSG) after DRM could effectively remove most of the deposited carbon and by-produce syngas. Subsequently, the small amount of carbon residue after the CSG step could be preferentially combusted by O 2 into CO 2 in flue gas, and then be captured by CaO instead of generating CO. This study demonstrates the feasibility and challenges of ICCU-DRM under simulated power plant flue gas conditions and provides potential insights for future investigation and deployment of this integrated process. [ABSTRACT FROM AUTHOR]

• The techno-economic analysis including mass balance, energy balance, CO cost, etc, confirmed ICCU better. • The Cost of CO 2 avoided of ICCU is much lower than that of CCU. • H 2 cost was the main contributor to the total cost. Currently, excessive CO 2 emissions have become a global challenge due to their influence on the climate. According to the Paris Agreement, global warming should be limited to 1.5 °C by 2100. Carbon capture and utilisation (CCU) are attractive as they can both reduce CO 2 content and utilise CO 2 as a carbon resource. However, in conventional CCU processes, CO 2 needs first to be extracted and purified for the following utilisation. In contrast, the recently reported Integrated Carbon Capture and Utilisation (ICCU) was designed to realise the overall process in one reactor, where CO 2 is captured by adsorbents (e.g., CaO) and utilised in-situ with the introduction of a reducing agent (e.g., H 2). This ICCU technology can promote CO 2 conversion with fewer intermediate steps, leading to a reduction in overall cost. Energy and economic analysis of ICCU are thus urgently required. According to several recent research, the operational cost of ICCU has been reported to be cheaper than that of CCU. However, a comprehensive view of ICCU is still expected due to further application. This paper focuses on comparing ICCU and conventional CCU processes based on Aspen simulations covering mass balance (i.e., CaCO 3 consumption, purge production, annual CO production), energy balance, the total annual cost and the CO cost, etc. Analysis shows that the ICCU process can produce more CO (1.20 Mt year−1), less purge (0.21 Mt year−1), and less consumption of CaCO 3 (0.62 Mt year−1) with higher energy efficiency (37.1 %) than the CCU process. The results also show that the total annual cost of ICCU is $867.07 million, corresponding to a total cost of CO of $720.25 per tonne. In contrast, CCU has higher costs, with a total annual cost of $1027.61 million and a total cost of CO of $1004.53 per tonne. The Cost of CO 2 Avoided of ICCU (317.11$/ton) is much lower than that CCU (1230.27 $/ton). Therefore, ICCU was confirmed as a better choice for further industrial applications. In addition, H 2 is shown to have a significant influence on economic performance, which remains a challenge for further application. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2) capture is critical for emission reduction. Biochar is a promising adsorbent for CO 2 capture. In this work, the effect of relative humidity and biochar activation with steam or KOH treatment on CO 2 capture was investigated. The results demonstrate that the biochar sample activated by KOH has a high CO 2 capture capacity (50.73 mg g−1). In addition, the biochar after 1.0 h of steam treatment showed a carbon capture capacity of 38.84 mg g−1. The results also show that the capture ability of biochar decreased as CO 2 concentration decreased from 100% to 15%. The relative humidity had a negative impact on CO 2 capture over biochar. The CO 2 capture capability of biochar materials treated by steam decreased by a range of 31.38%–62.89% as the relative humidity rose from 8.8% to 87.9%. Furthermore, the lifetime of biochar samples at various relative humidity shows that increased relative humidity had a negative impact on CO 2 adsorption due to water molecules occupying active sites. • KOH activated wood pellet biochar has a CO 2 capture capacity of 50.73 mg g−1. • CO 2 capture performance of Chemical activated biochar outperforms physically activated biochar. • High relative humidity has a negative effect on CO 2 adsorption of biochar. • Biochar shows higher stability under dry conditions than moisture conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mechanism of integrated carbon capture and utilization (ICCU) over 10 %NiCaO was investigated by the time-resolved operando XAS/DRIFTS/MS. • The influence of a reduction pretreatment on the process and the products formed was deeply investigated. • The Ni active species are oxidized by CO 2 in the 1st stage of ICCU (carbon capture) , leading to the formation of NiO and CO. • Heating 10% NiCaO to the operating temperature under hydrogen resulted in a switch of predominant product from CO to CH 4. An integrated carbon capture and utilization (ICCU) process present an ideal solution to address anthropogenic carbon dioxide (CO 2) emissions from fossil fuel-driven electricity production, allowing for capturing and subsequent utilization of CO 2 instead of current release into the atmosphere. Effective dual-functional materials (DFMs), through the combination of CO 2 sorbents and catalysts, can not only capture CO 2 but also convert it into higher-value chemicals, such as CH 4 or CO, under isothermal conditions within a single reactor are highly desirable for ICCU processes. In this study, we investigate the mechanism of ICCU over 10 %NiCaO by the time-resolved operando XAS/DRIFTS/MS and the influence of a reduction pretreatment on the process and the products formed. During the 1st stage of the ICCU process (carbon capture), CaO adsorbs CO 2 resulting in bicarbonate, carbonate, and formate species formation. At the same time, the Ni catalytic active species are oxidized by CO 2 , leading to the formation of NiO and CO. However, pre-treating the same DFM under hydrogen, during heating to operating temperature, resulted in a switch to CH 4 production, suggesting the presence of high levels of surface adsorbed H 2. During the 2nd stage of ICCU (CO 2 conversion), the NiO generated during capture is reduced by H 2 to metallic Ni, which facilitates the reduction of bicarbonates, carbonates, and formats, via H 2 dissociation, to produce and liberate gaseous CO. Thus, both adsorption and catalytic sites are regenerated for the subsequent ICCU cycle. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ni/supports-CaO are active in integrated CO 2 capture and reverse water–gas shift reaction. • The basicity of Ni/CeO 2 promotes the CO 2 adsorption of Ni/CeO 2 -CaO in ICCU-RWGS. • Ni/CeO 2 -CaO possesses high Ni dispersion and reducibility. • Stable and even self-optimizing cyclic ICCU-RWGS performance was achieved using Ni/CeO 2 -CaO. Integrated CO 2 capture and utilisation (ICCU) is a promising strategy for restricting carbon emissions and achieving carbon neutrality. Bifunctional combined materials (BCMs), containing adsorbents and active catalysts, are widely applied in this process. Producing syngas via reverse water–gas shift reaction (RWGS) and integrating with Fischer-Tropsch (F-T) synthesis is an attractive and valuable CO 2 utilisation route. This work investigated a series of Ni/support-CaO BCMs (supports = ZrO 2 , TiO 2 , CeO 2 and Al 2 O 3) for the integrated CO 2 capture and RWGS (ICCU-RWGS) process. The Ni/support-CaO BCMs were prepared by physically mixing various metal oxide supports loaded Ni with sol–gel derived CaO. The ICCU-RWGS performance (CO 2 conversion, CO yield and CO generation rate) of these BCMs followed the order during tested conditions (550–750 °C): Ni/CeO 2 -CaO > Ni/TiO 2 -CaO > Ni/ZrO 2 -CaO > Ni/Al 2 O 3 -CaO. A comprehensive characterisation of Ni/support materials showed that Ni/CeO 2 had the characteristics of stronger basicity, optimal Ni dispersion and improved NiO reducibility, which led to the outperforming ICCU-RWGS activity over Ni/CeO 2 -CaO (e.g. 56.1% CO 2 conversion, 2.68 mmol g−1 CO yield and ∼100% CO selectivity at 650 °C). Furthermore, the Ni/CeO 2 -CaO BCM showed a stable, yet, self-optimising catalytic performance during the cyclic ICCU-RWGS reaction over 20 cycles. The TEM characterisation suggested that was ascribed to the volume expansion and shrinkage of CaO in the cyclic adsorption–desorption altering the distance between the adsorbent and Ni/CeO 2 , resulting in an enhanced CO 2 conversion during the cycle. [ABSTRACT FROM AUTHOR]

• Highly dispersed sub-nanometer Ni clusters were produced in Ni-CeO 2 /CaO. • Synergies happened between highly dispersed Ni clusters and ceria oxygen vacancies. • CH 4 productivity was 1540 mmol g−1 Ni with 50.4% of CO 2 conversion. • The dual functional materials demonstrated high stability of ICCU. Integrated carbon capture and utilization (ICCU) presents an ideal solution to address anthropogenic carbon dioxide (CO 2) emissions from industry and energy sectors, facilitating CO 2 capture and subsequent utilization through conversion into high-value chemicals, as opposed to current release into the atmosphere. Herein, we report the synergistic coupling of porous CaO, as a sorbent for CO 2 capture, and Ni doped CeO 2 nanorods, as catalytic sites for CO 2 reduction. It is found that ceria is shown to possess the capacity for CO 2 utilization, however, critically it only results in the generation of CO due to the weak CO-ceria bonding. The addition of Ni active sites gives rise to CH 4 being the predominant product, via the strong interaction between Ni species and CO, which facilitates further reduction. Through tuning Ni loadings, we have evaluated the role of catalytic active site size, with a Ni loading of only 0.5 wt% providing optimal performance through the formation of sub-nanometer sized clusters. This near-atomic active site dispersion gives rise to CH 4 productivity and selectivity of 1540 mmol g−1 Ni and 85.8%, respectively, with this optimal combination of catalyst and sorbent demonstrating high stability over 10 cycles of ICCU process. These observations in parallel with the synergistic coupling of earth-abundant, low-cost materials (CaO and Ni) will have broad implications on the design and implementation of high efficiency, cost-effective ICCU materials and processes. [ABSTRACT FROM AUTHOR]

Porous materials with photochromic units are currently under investigation as light allows for environmentally friendly and highly energy-efficient control for gas separation and storage, chemical sensing, and drug delivery. In the application of photo-switching materials to CO 2 capture, researchers have tried to endow a diversity of porous materials such as metal-organic frameworks and porous organic polymers with photo-responsive units. This review highlights photochromic units and methods used for different types of photo-responsive adsorbents of CO 2 and some examples of adsorbents with photo-switching properties. These sorbents are also promising for application to direct air capture of CO 2. In particular, the cost of adsorbent regeneration could be reduced by using sorbents with light-induced regeneration. The key purpose of this review is to motivate more research into photo-switching sorbents for CO 2 capture with the control of capture or release by simply switching the light on and off. • Using light to regenerate the adsorbents is promising for carbon capture. • Photochromic units can be embedded into photo-switching sorbents. • Photo-switching metal-organic frameworks and porous organic polymers are reported. • Photo-switching sorbents may be applied to direct air capture of CO 2. [ABSTRACT FROM AUTHOR]

The distance between catalytic sites (Ni) and sorbents (CaO) on the performance of integrated CO 2 capture and utilization (ICCU) process is crucial important because the sorbents demonstrate a dramatic volume increase during carbonation reaction (1st stage of ICCU) and sequentially cover the catalytic sites and retard the CO 2 conversion (2nd stage of ICCU). Herein, we synthesized various Ni/CaO-based dual functional materials (DFMs) with different distances between active sites and sorbents to provide different volume spaces for the growth of CaCO 3 during the carbonation reaction. It is found that both 1%NiCaO and 10%NiCaO synthesized by a one-pot method exhibited a low CO 2 conversion (38% and 45%, respectively) and CH 4 selectivity (58% and 69%, respectively) as the distance between catalytic sites and sorbents was so close that the Ni active sites were covered by the formed CaCO 3 during carbonation reaction. With the increase of the distance by physical mixing method, the CO 2 conversion and CH 4 selectivity of 1%Ni/CeO 2 -CaO-phy were largely increased to 62% and 84%, respectively at 550 °C and atmospheric pressure when captured CO 2 from 15% CO 2 /N 2. This is attributed to the fact that the Ni active sites were still well dispersed on the surface of CeO 2 nanorods instead of being covered by the newly formed CaCO 3. [ABSTRACT FROM AUTHOR]

• AD digestate was converted into biochar-based sorbents of CO 2 easily. • A one-step method of introducing N into biochar was studied. • Adding urea enhanced CO 2 uptake ability of biochar. • AD digestate has potential application for carbon capture. Digestate from Anaerobic Digestion (AD) is a very common waste produced by European biogas plants and its current method of reuse is as a fertilizer or as soil amendment. This in turn however gives rise to some other environmental concerns which include greenhouse gas emissions and volatilization of ammonia causing ammonia pollution. Biochar is an environmentally friendly and low-cost product for CO 2 capture and sequestration. Thus, we have provided one simple method to convert AD digestate into biochar-based sorbents of CO 2. In addition, the nitrogen-functionalised porous carbon has been reported to be effective in improving the uptake of CO 2. However, most of them were prepared using multiple steps. In this work, N-doped biochar was prepared by a one-step method of modifying AD digestate by urea. The results show that the addition of N can increase CO 2 uptake significantly. Thus, the adsorbent modified by urea with a ratio of 1:1 results in the highest CO 2 uptake capacity (1.22 mmol g−1), indicating digestate's potential application for carbon capture and storage. [ABSTRACT FROM AUTHOR]