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In recent years, the rapid consumption of fossil fuels has brought about the energy crisis and excess CO2 emission, causing a series of environmental problems. Photocatalytic CO2 reduction technology can realize CO2 emission reduction and fuel regeneration, which alleviates the energy crisis and environmental problems. As the most widely used LDH material in commercial application, MgAl-layered double hydroxide (MgAl-LDH) already dominates large-scale production lines and has the potential to be popularized in CO2 photoreduction. The adjustable component, excellent CO2 adsorption performance, and unique layer structure of MgAl-LDH bring specific advantages in CO2 photoreduction. This review briefly introduces the theory and reaction process of CO2 photocatalytic reduction, and summarizes the features and drawbacks of MgAl-LDH. The modification strategies to overcome the drawbacks and improve photocatalytic activity for MgAl-LDH are elaborated in detail and the development perspectives of MgAl-LDH in the field of CO2 photoreduction are highlighted to provide a guidance for future exploration. [ABSTRACT FROM AUTHOR]

Calcium looping (CaL) has being considered a CO 2 capture technology with great promise because of its wide suitability and low-cost. In this work, the Ca(OH) 2 core was coated with porous alumina coverings via a dip-coating approach to produce CaO-based sorbent pellet with core-shell structure. The coating shell was prepared by evaporation-induced self-assembly sol-gel strategy using P123 as the pore-forming agent with different acidic conditions (i.e., acid-alcohol ratio varied from 0.05 to 3). It reveals that the cyclic CO 2 capture performance of core-shell structured CaO-based sorbent pellets decreases with the increase of acidity of sol-gel using for covering spherical cores. When coating gel with excessive acidity, the formation of dense alumina shell and the irreversible chlorination inactivation, which together lead to the low cyclic CO 2 capture performance. Particularly, the CO 2 capture capability of core-shell structured CaO-based sorbent pellets whose shell gel used for coating in low acid-alcohol ratio of 0.05 is as high as 1.4 times that of non-shell CaO-based pellets after 17 cycles. Meanwhile, the core-shell structured CaO-based sorbent holds good potentials to inhibit the adverse impact of in-situ coal combustion compared with conventional non-shell pellets in practical CaL system. [Display omitted] • Core-shell structured CaO-based pellets were prepared by wet coating method. • Acid-alcohol ratio closely affects the morphology of the outer alumina shell. • Excessive acidity causes dense outer shell and irreversible chlorination inactivation. • Core-shell structured pellets inhibit adverse impact of in-situ coal combustion. [ABSTRACT FROM AUTHOR]

In this work, we have investigated the effect of different supports (activated carbon (AC), α-Al 2 O 3 , ZSM-5 and SiO 2) on the plasma-catalytic synthesis of ammonia (NH 3) from N 2 and H 2 over Ru-based catalysts in a dielectric barrier discharge (DBD) plasma reactor. Compared with the NH 3 synthesis using plasma alone, the presence of the Ru-based catalysts in the DBD reactor significantly enhanced the NH 3 production and energy yield by 163%–387.6% with a sequence of Ru/AC > Ru/ZSM-5 > Ru/α-Al 2 O 3 > Ru/SiO 2. The effect of different operating parameters on the plasma-catalytic NH 3 synthesis over Ru/AC was also examined. N 2 adsorption-desorption experiment, X-ray diffraction analysis and temperature-programmed desorption of CO 2 were performed to get insights into the structure-performance relationships between the plasma-catalytic NH 3 synthesis and Ru-based catalysts with different supports. Both textural properties and the basicity of the Ru/AC catalyst contributed to the enhanced NH 3 production in the hybrid plasma-catalytic system. [Display omitted] • Plasma-catalytic ammonia synthesis over Ru-based catalysts was investigated. • The effect of different supports on the plasma-catalytic ammonia production was evaluated. • Coupling of plasma with Ru-based catalysts significantly enhanced ammonia production and energy yield. • Ru/AC showed the highest ammonia concentration and energy yield. [ABSTRACT FROM AUTHOR]

Porous carbons produced using poplar sawdust are promising CO 2 adsorbent applied under ambient conditions due to the low-cost preparation approach. CO 2 uptake capability of the porous carbons produced from poplar sawdust can be effectively enhanced via doping an approximate amount of microalgae. The N-doped porous carbon produced from poplar sawdust using microalgae as N-doping source (microalgae/poplar sawdust=0.5:1) possesses an excellent capacity of 4.14 mmol·g−1 for CO 2 uptake, nearly over 1.7 times that of the carbon without N-doping. The improved performance for CO 2 uptake of porous carbons is mainly ascribed to the two-fold effect of microalgae doping: (i) generating extensive narrow pores and channels within the porous carbons owe to co-pyrolysis; (ii) introduction of N-containing moieties derived from the intrinsic N of microalgae increasing the surface polarity and alkalinity. The N-doped porous carbon granules derived from poplar sawdust are inferior to the powdered porous carbons for CO 2 adsorption due to the destroyed structure. They still maintain the relatively desirable capability for CO 2 adsorption (~3.0 mmol·g−1 during 5 cycles) and good mechanical property (10.96 ± 1.43 Mpa). Comprehensively considering the advantaged properties (low-pressure drop, high bulk density) required for practical application, the N-doped porous carbon granules derived from poplar sawdust with low-doping of renewable microalgae possess strong practicability. [Display omitted] • Microalgae replaces the chemical N-containing reagents as the N-doping source. • Microalgae doping plays a two-fold role in enhancing CO 2 adsorption for porous carbon. • N-doped, sawdust-derived porous carbons exhibit desirable CO 2 adsorption capacity. • N-doped, sawdust-derived porous carbon extrudates possess superior practicability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Limestone calcined under in-situ combustion of raw, ammonium acetate- and HCl/HF acid-washed coal. • High temperature, alkali metals and coal ash impair CO 2 uptake of limestone sorbent. • Limestone pellet is less negatively affected by in-situ coal combustion than powder. • Cellulose-templated limestone pellet exhibits good CO 2 uptake under in-situ coal combustion. Calcium Looping technology is one of the most promising post-combustion CO 2 capture technologies. However, the fine CaO-based sorbents are prone to elutriate in the fluidized-bed reactors. The in-situ combustion of coal in the calciner will greatly affect the performance of the regenerated CaO. In this work, extrusion-spheronization method was adopted to prepare limestone-based pellets to mitigate the issue of elutriation. To clearly elucidate the deactivation mechanism of CaO-based sorbents under in-situ coal combustion, the CaO-based sorbents mixed with raw, ammonium acetate-washed, HCl/HF acid-washed coal were conducted respectively. The CaO-based sorbent pre-calcined under in-situ ammonium acetate-washing and HCL/HF acid-washing coal combustion is superior to that pre-calcined under in-situ raw coal combustion for cyclic CO 2 capture. The elimination of the low-melting alkali metals (i.e., Na, K) and residual coal ash contributes to the improved cyclic CO 2 capture performance of CaO-based sorbent. Moreover, the adverse effect of in-situ coal combustion on limestone-based pellet is less serious than that on limestone powder due to the outer layer of the pellet protecting the active CaO inside from contamination by in-situ coal combustion. Furthermore, the cellulose-modified, limestone-based sorbent pellet exhibits quite prominent advantage on cyclic CO 2 capture performance, particularly in the case of pre-calcination under the condition of in-situ coal combustion. [ABSTRACT FROM AUTHOR]

• Impregnated layer solution combustion contributes to enhancing CO 2 capture stability. • CaZrO 3 exhibits excellent property on improving CO 2 capture stability of limestone. • 10 wt% of CaZrO 3 sufficiently provides effective structural stability for limestone. Calcium looping is an effective post-combustion technology for CO 2 separation from flue gas due to its low-cost and highly accessible sorbent raw material (i.e., limestone). However, limestone easily occurs serious sintering during multiple high-temperature carbonation/calcination cycles. Here, three types of modification mode, including acetic acid acidification, wet and dry solution-impregnated cigarette butts-assisted combustion methods, were adopted to enhance the cyclic stability of limestone. The impregnated layer solution combustion mode is superior to acid acidification, which is mainly ascribed to the heat released from the combustion of cigarette butt playing the role of thermal pretreatment, thereby stabilizing the pore structure of limestone-derived sorbents. Incorporating different inert supports can further enhance the cyclic stability of limestone-derived sorbents synthesized by wet solution-impregnated cigarette butts-assisted combustion. The effectiveness of several inert supports in improving the cyclic stability of limestone-derived adsorbents is listed as follows: CaZrO 3 > MgO > Ca 12 Al 14 O 33 > CaMn 2 O 4. Moreover, the loading content of CaZrO 3 within limestone-derived sorbents was further optimized, and it was found that 10 wt% of CaZrO 3 sufficiently provides stable framework to inhibit high-temperature sintering (∼0.525 g-CO 2 /g-sorbent after 20 cycles). The uniformly dispersed CaZrO 3 support at the nanocrystalline scale effectively inhibiting sintering is responsible for the excellent cyclic CO 2 capture capability of CaZrO 3 -supported sorbents. [ABSTRACT FROM AUTHOR]

[Display omitted] • The SO 3 removal performance of 11 absorbents was studied. • There was obvious competition between SO 2 and SO 3 in the absorption process of SO 3 by Na 2 CO 3. • Oxygen prevented SO 3 from reacting with Na 2 CO 3 by oxidizing Na 2 SO 3 to form Na 2 SO 4. • The presence of HCl had an inhibitory effect on the absorption of SO 3. • When SO 2 , HCl and SO 3 existed simultaneously, the inhibition of SO 2 on the adsorption of SO 3 by Na 2 CO 3 was dominant, the inhibition effect of SO 2 on SO 3 and the inhibition of HCl on SO 3 did not accumulate. SO 3 in coal-fired flue gas will cause equipment corrosion and the emission of sulfuric acid mist. The complex component in the flue gas will affect the performance of alkaline absorbent. In this study, a fixed bed reactor was used to evaluate the absorption performance of SO 3 by a variety of absorbents. Then, on this basis, the competition between SO 3 and SO 2 , SO 3 and HCl were studied by the fixed bed reactor. The effect of oxygen on the competitive absorption of SO 3 and SO 2 by absorbents was also investigated. Further, when SO 2 , HCl and SO 3 existed simultaneously, the competitive reactions between multiple gases were investigated. The influence of SO 2 and HCl on SO 3 absorption was evaluated. Carbonate absorbents had stronger absorption capacity than other absorbents. In the adsorption process of SO 3 by Na 2 CO 3 , the presence of SO 2 inhibited the absorption of SO 3 by Na 2 CO 3 , and oxygen oxidized Na 2 SO 3 to produce Na 2 SO 4 , which affected the reaction between SO 3 and Na 2 CO 3.There was strong competition between SO 3 and SO 2. In the process of SO 3 adsorption by Na 2 CO 3 , the presence of HCl had an inhibitory effect on the absorption of SO 3 , SO 3 could significantly inhibit the absorption of HCl. When SO 2 , HCl and SO 3 existed simultaneously, SO 2 had a stronger influence on the adsorption of SO 3 by Na 2 CO 3 and the presence of HCl had little inhibition on the absorption of SO 3 by Na 2 CO 3. The inhibition effect of SO 2 on SO 3 and the inhibition of HCl on SO 3 did not accumulate. [ABSTRACT FROM AUTHOR]

Converting CO 2 into renewable fuel via photocatalysis is of significance to solving the energy crisis and climate change. However, the limited electron transfer in single catalysts always limits the reduction reaction. In this work, a p-n heterojunction was constructed between Cr doped MgAl–LDH (abbreviated as LDH) and Co 3 O 4 for visible-light-driven fuel production. Since LDH and Co 3 O 4 both have the sufficient potentials to drive CO 2 photoreduction, the constructed type-II heterojunction is more favorable for electron utilization efficiency. The optimal Co 3 O 4 /LDH heterojunction exhibited the highest CO evolution rate of 7.42 μmol•g−1•h−1 and a CO selectivity of 90.5% with TEOA as sacrificial agent. The further characterizations highlight that the addition of Co 3 O 4 greatly improves the light absorption and the heterojunction effectively promotes the reverse migration of electrons and holes. This work investigates and verifies the designed type-II heterojunction based on MgAl–LDH, which has the guidance for the design of heterojunction catalysts and promotes the practical application of MgAl–LDH in photocatalytic region. [Display omitted] • Co 3 O 4 /Cr doped MgAl-LDH p-n heterojunction was constructed for CO 2 photoreduction. • Suitable type-II heterojunction is favorable for electron utilization efficiency. • Heterojunction greatly improves the light absorption and charge migration. • Com-Co 3 O 4 /LDH is plagued by the unmatched band and insufficient charge transfer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Al-stabilized CaO-based sorbents produced by impregnated layer solution combustion. • Ca 12 Al 14 O 33 grains provide an effective inert framework for the synthetic sorbents. • Graphite-moulding method can prepare highly efficient CaO-based sorbent pellets. • Al-stabilized CaO-based sorbent pellets exhibit desirable property for CO 2 capture. Calcium looping (CaL) process is recognized as one of the most promising CO 2 capture technologies. However, the CaO-based sorbents commonly encounter serious sintering and elutriation problem during CO 2 capture cycles. In this work, Al-stabilized, CaO-based sorbents were synthesized by the impregnated layer solution combustion method, and cigarette butt was selected as the porous reactive skeleton. The Al-stabilized, CaO-based sorbent containing 15 wt% of Al 2 O 3 exhibits the highly stable CO 2 capture performance, whose CO 2 capture capacity after 20 cycles is almost the same as its initial capacity, ∼0.354 g/g. It is mainly attributed to the synergistic effect of thermal pretreatment (cigarette butt-assisted combustion) and incorporation of Al-based stabilizer (i.e., Ca 12 Al 14 O 33) provide a stable inert framework for the synthetic sorbents, ensuring their highly stable capability for CO 2 sorption during cycles. Further, graphite-moulding is a facile and energy-saving approach to make Al-stabilized, CaO-based sorbent powders into pellets to enhance its resistance to elutriation. The produced sorbent pellets (85 wt% CaO/15 wt% Al 2 O 3) exhibit excellent long-term CO 2 capture capacity (∼0.248 g/g after 49 cycles) and high compression strength of 18.47 ± 3.47 MPa. Therefore, the combined method involved of impregnated layer solution combustion and graphite-moulding is promising to produce highly efficient CaO-based CO 2 sorbent pellets used in CaL. [ABSTRACT FROM AUTHOR]

Various value-added chemicals such as formic acid, carbon monoxide, methane, methanol, have been obtained using CO 2 as a feedstock. However, formaldehyde generation from CO 2 is less reported. Here, we performed CO 2 hydrogenation with H 2 in additive-free water and used layered double hydroxide supported Ru as the heterogeneous catalyst. It was found that gaseous CO 2 and H 2 could be efficiently and selectively converted to formaldehyde dissolved in water even at room temperature with ambient pressure. The highest gaseous CO 2 conversion of 89.7% and a formaldehyde yield of 58.7% were achieved using a Ru/LDH-red catalyst in water at 30 °C with 10 bar CO 2 and 10 bar H 2. Combined with experimental and theoretical studies, HCOOH was found as the important reaction intermediate. The rich surface –OH of LDH and hybrid electronic state of Ru over Ru/LDH-red catalyst resulted in highly efficient HCHO formation. Our findings offer opportunities to one energy-efficient formaldehyde synthesis method. [Display omitted] • Formaldehyde was formed from aqueous CO 2 over a Ru/LDH catalyst under mild conditions. • CO 2 reduction activity and selectivity was regulated by the states of Ru. • The catalytic route was illustrated by DRIFTs measurements and DFT calculations. • Formic acid is one important intermediate during CO 2 hydrogenation to formaldehyde. [ABSTRACT FROM AUTHOR]

Developing efficient catalysts with good resistance to complex flue gas is essential for VOCs removal in coal-fired flue gas. In this study, by exploring the effect of transition metal oxide additive, metal loading and bimetallic synergy on toluene oxidation in coal-fired flue gas, 10Cu-3V/γ-Al 2 O 3 is identified as the optimal catalyst. It achieves 90% of CO 2 generation at 350 ℃, which is decreased by ca. 46 ℃ compared with 13Cu/γ-Al 2 O 3. And it also exhibits good resistance to H 2 O and good stability. ICP-OES, N 2 adsorption-desorption isotherms, XRD, TEM, XPS, EPR and H 2 -TPR analyses were applied to characterize the catalyst composition and physicochemical properties. Doping V into 13Cu/γ-Al 2 O 3 not only leads to better dispersity of CuO and homogeneous elements distribution that benefits to produce more active centers, but also constitutes the redox cycle of V5+ + Cu+ ↔ V4+ + Cu2+ which induces more surface chemical oxygen (O sur). Moreover, since SO 2 is the main inhibiting factor in toluene oxidation, the SO 2 poisoning mechanism was illustrated by XPS, TG and in situ DRIFT analyses in depth. [Display omitted] • Temperature at 90% of CO 2 generation is decreased by ca. 46 ℃ after introducing V. • Temperature at 90% of CO 2 generation is unchanged (ca. 350 ℃) after introducing H 2 O. • The relationship between performance and physicochemical properties is discussed. • The inhibition mechanism of SO 2 is reasonably speculated. [ABSTRACT FROM AUTHOR]

The CO 2 emissions brought about by traditional volatile organic compounds (VOCs) reduction technologies have become an urgent problem in the carbon neutrality era. The combination of adsorption and photocatalysis could meet the requirements for co-ordinated control of VOCs and CO 2 emissions. This review summarizes and analyzes the research results of carbon material-TiO 2 cross-linked structure for the photocatalytic degradation of VOCs and reduction of CO 2. This article first systematically analyzes the impact of environmental factors on photocatalytic efficiency, summarizes the characteristics of different modification methods. Then, it further summarizes the main directions of carbon material modification, and focuses on the research on the functional cross-linking of different carbon materials and TiO 2. Finally, this paper indicates the photocatalytic degradation/reduction pathways of different reactants, and analyzes the synergistic mechanism of carbon material-TiO 2. This review will provide parameter support and optimization suggestions for the research of carbon materials-TiO 2 nano-composites, and provide foundation for future researches. [Display omitted] • The synergistic mechanism of carbon material-TiO 2 has been summarized. • The best doping ratios of metal/non-metal elements and heterojunctions are given. • The optimal ratios of carbon materials in the cross-linked structure are given. • The adsorption-photocatalytic properties of carbon materials-TiO 2 are analyzed. [ABSTRACT FROM AUTHOR]

Li 4 SiO 4 sorbents have exhibited promising prospects for high-temperature CO 2 capture. However, conventional Li 4 SiO 4 using solid-state reaction method usually exhibits dense structures with barren porosity, limiting the CO 2 sorption. To solve this problem, a sol-mixing method using organometallic lithium precursors was employed to produce 'new' Li 4 SiO 4 sorbents with improved CO 2 sorption performance. The obtained Li 4 SiO 4 from lithium salicylate precursor exhibited enhanced specific surface area and modified micromorphology compared to the conventional Li 4 SiO 4. The morphology showed that the 'new' Li 4 SiO 4 possessed many fluff-like folds on the surface, in comparison with the smooth surfaces of conventional sorbent. As a result, the 'new' sorbent exhibited CO 2 uptake of ~0.15 g/g, which is more than three times as high as that of the conventional one. Furthermore, the CO 2 uptake was further enhanced to 0.32 g/g by K 2 CO 3 doping. After granulation, the pellets also presented good CO 2 sorption performance as well as excellent mechanical strength for practical applications. Generally, the good sorption performance and excellent mechanical strength demonstrated the effectiveness of sol-mixing method and lithium salicylate as precursors for the production of efficient Li 4 SiO 4 sorbents. • Li 4 SiO 4 was prepared using lithium salicylate precursor via sol-mixing method. • The new sorbent exhibited the morphology with many fluff-like folds on the surface. • The CO 2 uptake of the new sorbent was over 3 times that of the conventional Li 4 SiO 4. • The granulated sorbents showed both good sorption performance and mechanical strength. [ABSTRACT FROM AUTHOR]

It has been widely acknowledged that the Li 4 SiO 4 -based adsorbents with smaller particle size and tailored structure will certainly exhibit superior CO 2 capture performance. In this work, a novel two-phase synthesis method was proposed to produce tailored micro-scale Li 4 SiO 4 -based adsorbents with ultrafast CO 2 capture rate. The effects of synthetic temperature on the phase compositions, the chemical bonds, the pore structure, the surface morphology and the CO 2 capture performance of obtained adsorbents were systematically investigated. It is found that the increase of temperature during synthesis process could promote the Li 4 SiO 4 content of obtained adsorbents. Nevertheless, higher temperature also leads to the aggravation and sintering of particles, thus hindering the capacity of adsorbents. Examining the pros and cons, the adsorbent calcined at 600 °C shows the greatest morphology consisted of hollow-structured microspheres with a uniform diameter of 1–2 μm and exhibits the fastest adsorption rate as well as the highest adsorption capacity (~ 0.184 g CO 2 /g adsorbent within only 5 min's adsorption under 15 vol% CO 2), leading to a superior Li 4 SiO 4 conversion as high as ~80%. In a word, this two-phase method is promising in the future production of Li 4 SiO 4 -based microspheres for high-efficient and ultrafast CO 2 capture. • A novel & facile two-phase method is proposed to produce Li 4 SiO 4 -based microsphere. • The synthetic temperature has both positive and negative influences on adsorbents. • Adsorbent calcined at 600 °C has the greatest surface area and surface morphology. • L600 has a great capacity of ~0.184 g/g within only 5 min's sorption under 15% CO 2. [ABSTRACT FROM AUTHOR]