Catalyst-TiO(OH)2 could drastically reduce the energy consumption of CO2 capture

Nanoporous Metatitanic acid on γ-Al2O3 aerogel for higher CO2 adsorption capacity and lower energy consumption

Carbon dioxide capture has become an important issue in reducing atmospheric heat these days. In this study, adsorption of carbon dioxide by aerogel Gamma Alumina-Metatitanic Acid has been investigated and optimized. Morphological and structural analyses such as BET, FESEM, FT-IR, and XRD have also been conducted. In addition, Response surface methodology has been applied in order to achieve the optimal conditions, using a five-level Central composite design. The highest amount of adsorption, 12.874 (mmol/g), was recorded at a temperature of 20 (°C), pressure of 7 (bar), and 25 (%wt) of Metatitanic Acid. This was approximately 11.46% and 4.84% higher than those of mesoporous MgO and 4Azeolite, respectively. Regeneration of the adsorbent was also studied at different temperatures and process durations. Metatitanic acid, as a catalyst, reduces the temperature and regeneration time of the adsorbent by creating active sites and surface hydroxyl groups. It also lowers the required activation energy and enhances the thermal conductivity of the composite material. The optimal result was achieved at a temperature of 100 (°C) and a duration of 30 (min). Finally, isothermal and thermodynamic experiments were conducted to establish the most accurate predictive model and conditions, including Enthalpy, Entropy, and Gibbs free energy. The results indicate that the Freundlich model aligned well with the laboratory findings. Additionally, the negative values of Enthalpy, Entropy, and Gibbs free energy suggested that the adsorption process was physical, exothermic, and spontaneous.

Comparative Review for Enhancing CO2 Capture Efficiency with Mixed Amine Systems and Catalysts

This study investigates methods to enhance the efficiency of CO2 capture using organic amine absorption and compares the performance of traditional and novel amine solvents. It reviews various single-component and mixed amine absorbents, as well as catalysts used in these methods, highlighting the superiority of mixed amine absorbents over single-component amine absorbents in CO2 absorption and desorption. Additionally, the study explores the catalytic mechanisms and effects of catalysts in the CO2 absorption/desorption process with amine solvents and provides an outlook on future research directions. The aim is to promote the widespread adoption of organic amine absorption technology in industrial applications and to contribute to the development of more sustainable and efficient CO2 capture technologies.

Carbon Dioxide Capture by Niobium Polyoxometalate Fragmentation

High oxidation state metal cations in the form of oxides, oxoanions, or oxoperoxoanions have diverse roles in carbon dioxide removal (direct air capture and point source). Features include providing basic oxygens for chemisorption reactions, direct binding of carbonate, and catalyzing low-temperature CO2 release to regenerate capture media. Moreover, metal oxides and aqueous metal-oxo species are stable in harsh, point-source conditions. Here, we demonstrate aqueous niobium polyoxometalate (POM) carbon capture ability, specifically [Nb6O19]8-, Nb6. Upon exposure of aqueous Nb6 to CO2, Nb6 fragments and binds chemisorbed carbonate, evidenced by crystallization of Nb-carbonate POMs including [Nb22O53(CO3)16]28-and [Nb10O25(CO3)6]12-. While Rb/Cs+ counter cations yield crystal structures to understand the chemisorption processes, K+ counter cations enable higher capture efficiency (based on CO3/Nb ratio), determined by CHN analysis and thermogravimetry-mass spectrometry of the isolated solids. Sum frequency generation spectroscopy also showed higher carbon capture efficiency of the K-Nb6 solutions at the air-water interface, while small-angle X-ray scattering (SAXS) provided insights into the role of the alkalis in influencing these processes. Tetramethylammonium counter cations, like K+, demonstrate high efficiency of carbonate chemisorption at the interface, but SAXS and Raman of the bulk showed a predominance of a Nb24-POM (HxNb24O72, x ∼ 9) that does not bind carbonate. Control experiments show that carbonate detected at the interface is Nb-bound, and the Nb-carbonate species are stabilized by alkalis, demonstrating their supporting role in aqueous Nb-POM CO2 chemisorption. Of fundamental importance, this study presents rare examples of directing POM speciation with a gas, instead of liquid phase acid or base.

Silicon photocathode functionalized with osmium complex catalyst for selective catalytic conversion of CO2 to methane

Solar-driven CO2 reduction to yield high-value chemicals presents an appealing avenue for combating climate change, yet achieving selective production of specific products remains a significant challenge. We showcase two osmium complexes, przpOs, and trzpOs, as CO2 reduction catalysts for selective CO2-to-methane conversion. Kinetically, the przpOs and trzpOs exhibit high CO2 reduction catalytic rate constants of 0.544 and 6.41 s-1, respectively. Under AM1.5 G irradiation, the optimal Si/TiO2/trzpOs have CH4 as the main product and >90% Faradaic efficiency, reaching -14.11 mA cm-2 photocurrent density at 0.0 VRHE. Density functional theory calculations reveal that the N atoms on the bipyrazole and triazole ligands effectively stabilize the CO2-adduct intermediates, which tend to be further hydrogenated to produce CH4, leading to their ultrahigh CO2-to-CH4 selectivity. These results are comparable to cutting-edge Si-based photocathodes for CO2 reduction, revealing a vast research potential in employing molecular catalysts for the photoelectrochemical conversion of CO2 to methane.

Cerium-MOF-Derived Composite Hierarchical Catalyst Enables Energy-Efficient and Green Amine Regeneration for CO2 Capture

The excessive energy consumed restricts the application of traditional postcombustion CO2 capture technology and limits the achievement of carbon-neutrality goals. Catalytic-rich CO2 amine regeneration has the potential to accelerate proton transfer and increase the energy efficiency in the CO2 separation process. Herein, we reported a Ce-metal-organic framework (MOF)-derived composite catalyst named HZ-Ni@UiO-66 with a hierarchical structure, which can increase the CO2 desorbed amount by 57.7% and decrease the relative heat duty by 36.5% in comparison with the noncatalytic monoethanolamine (MEA) regeneration process. The composite catalyst of the CeO2 coating from the UiO-66 precursor on the HZ-Ni carrier shows excellent stability with a long lifespan. The HZ-Ni@UiO-66 catalyst also shows a universal catalytic effect in typical blended amine systems with a large cyclic capacity. The HZ-Ni@UiO-66 catalyst effectively decreases the energy barrier of the CO2 desorption reaction to reduce the time required to reach thermodynamics, consequently saving the energy consumption generated by water evaporation. This research provides a new avenue for advancing amine regeneration with less heat duty at low temperatures.

Synergistic Catalysis of SO42-/TiO2-CNT for the CO2 Desorption Process with Low Energy Consumption

To address the issue of high energy consumption associated with monoethanolamine (MEA) regeneration in the CO2 capture process, solid acid catalysts have been widely investigated due to their performance in accelerating carbamate decomposition. The recently discovered carbon nanotube (CNT) catalyst presents efficient catalytic activity for bicarbonate decomposition. In this paper, bifunctional catalysts SO42-/TiO2-CNT (STC) were prepared, which could simultaneously catalyze carbamate and bicarbonate decomposition, and outstanding catalytic performance has been exhibited. STC significantly increased the CO2 desorption amount by 82.3% and decreased the relative heat duty by 46% compared to the MEA-CO2 solution without catalysts. The excellent stability of STC was confirmed by 15 cyclic absorption-desorption experiments, showing good practical feasibility for decreasing energy consumption in an industrial CO2 capture process. Furthermore, associated with the results of experimental characterization and theoretical calculations, the synergistic catalysis of STC catalysts via proton and charge transfer was proposed. This work demonstrated the potential of STC catalysts in improving the efficiency of amine regeneration processes and reducing energy consumption, contributing to the design of more effective and economical catalysts for carbon capture.

Sulfur Migration Enhanced Proton-Coupled Electron Transfer for Efficient CO2 Desorption with Core-Shelled C@Mn3O4

Transforming hazardous species into active sites by ingenious material design was a promising and positive strategy to improve catalytic reactions in industrial applications. To synergistically address the issue of sluggish CO2 desorption kinetics and SO2-poisoning solvent of amine scrubbing, we propose a novel method for preparing a high-performance core-shell C@Mn3O4 catalyst for heterogeneous sulfur migration and in situ reconstruction to active -SO3H groups, and thus inducing an enhanced proton-coupled electron transfer (PCET) effect for CO2 desorption. As anticipated, the rate of CO2 desorption increases significantly, by 255%, when SO2 is introduced. On a bench scale, dynamic CO2 capture experiments reveal that the catalytic regeneration heat duty of SO2-poisoned solvent experiences a 32% reduction compared to the blank case, while the durability of the catalyst is confirmed. Thus, the enhanced PCET of C@Mn3O4, facilitated by sulfur migration and simultaneous transformation, effectively improves the SO2 resistance and regeneration efficiency of amine solvents, providing a novel route for pursuing cost-effective CO2 capture with an amine solvent.

Embedded Mo/Mn Atomic Regulation for Durable Acidity-Reinforced HZSM-5 Catalyst toward Energy-Efficient Amine Regeneration

Metal-molecular sieve composites with high acidity are promising solid acid catalysts (SACs) for accelerating sluggish CO2 desorption processes and reducing the energy consumption of CO2 chemisorption systems. However, the production of such SACs through conventional approaches such as loading or ion-exchange methods often leads to uncontrolled and unstable metal distribution on the catalysts, which limits their pore structure regulation and catalytic performance. In this study, we demonstrated a feasible strategy for improving the durability, surface chemical activity, and pore structure of metal-doped HZSM-5 through bimetallic Mo/Mn modification. This strategy involves the immobilization of Mo-O-Mn species confined in an MFI structure by regulating MoO42- anions and Mn2+ cations. The embedded Mn/Mo species of low valence can strongly induce electron transfer and increase the density of compensatory H+ on the MoMn@H catalyst, thereby reducing the CO2 desorption temperature by 8.27 °C and energy consumption by 37% in comparison to a blank. The durability enhancement and activity regulation method used in this study is expected to advance the rational synthesis of metal-molecular sieve composites for energy-efficient CO2 capture using amine regeneration technology.

Nonacid Carbon Materials as Catalysts for Monoethanolamine Energy-Efficient Regeneration

In the CO₂ capture process, solid acid catalysts have been widely adopted to decrease energy consumption in the amine regeneration process owing to abundant acid sites. However, acid sites unavoidably degenerate in the basic amine solution. To address the challenge, nonacid carbon materials including carbon molecular sieves, porous carbon, carbon nanotubes, and graphene are first proposed to catalyze amine regeneration. It is found that carbon materials can significantly increase the CO₂ desorption amount by 47.1-72.3% and reduce energy consumption by 32-42%. In 20 stability experiments, CO₂ loading was stable with the max difference value of 0.01 mol CO₂/mol monoethanolamine (MEA), and no obvious increase in the relative heat duty (the maximum difference is 4%) occurred. The stability of carbon materials is superior to excellent solid acid catalysts, and the desorption performance is comparable. According to the results of theoretical calculation and experimental characterization, the electron-transfer mechanism of nonacid carbon materials is proposed, which is not only beneficial for MEA regeneration but also the probable reason for the stable catalytic activity. Owing to the excellent catalytic performance of carbon nanotube (CNT) in the HCO₃^- decomposition, nonacid carbon materials are quite promising to enhance the desorption performance of novel blend amines, which will further reduce the cost of carbon capture in the industry. This study provides a new strategy to develop stable catalysts used for amine energy-efficient regeneration.

Sn-Ag Synergistic Effect Enhances High-Rate Electrocatalytic CO2 -to-Formate Conversion on Porous Poly(Ionic Liquid) Support

The electrocatalytic transformation of carbon dioxide (CO₂ ) to formate is a promising route for highly efficient conversion and utilization of CO₂ gas, due to the low production cost and the ease of storage of formate. In this work, porous poly(ionic liquid) (PPIL)-based tin-silver (Sn-Ag) bimetallic hybrids (PPIL^m -Sn_x Ag_{10- x} ) are prepared for high-performance formate electrolytic generation. Under optimal conditions, an excellent formate Faradaic efficiency of 95.5% with a high partial current density of 214.9 mA cm^-2 is obtained at -1.03 V (vs reversible hydrogen electrode). Meanwhile, the high selectivity of formate (>≈83%) is maintained in a wide potential range (>630 mV). Mechanistic studies demonstrate that the presence of Ag-species is vital for the formation, maintenance, and high dispersion of tetravalent Sn(IV)-species, which accounts for the active sites for CO₂ -to-formate conversion. Further, the introduction of Ag-species significantly enhances the activity by increasing the electron density near the Fermi energy level.

Mesoporous MgO enriched in Lewis base sites as effective catalysts for efficient CO2 capture

Capturing CO₂ has become increasingly important. However, wide industrial applications of conventional CO₂ capture technologies are limited by their slow CO₂ sorption and desorption kinetics. Accordingly, this research is designed to overcome the challenge by synthesizing mesoporous MgO nanoparticles (MgO-NPs) with a new method that uses PEG 1500 as a soft template. MgO surface structure is nonstoichiometric due to its distinctive shape; the abundant Lewis base sites provided by oxygen vacancies promote CO₂ capture. Adding 2 wt % MgO-NPs to 20 wt % monoethanolamine (MEA) can increase the breakthrough time (the time with 90% CO₂ capturing efficiency) by ∼3000% and can increase the CO₂ absorption capacity within the breakthrough time by ∼3660%. The data suggest that MgO-NPs can accelerate the rate and increase CO₂ desorption capacity by up to ∼8740% and ∼2290% at 90 °C, respectively. Also, the excellent stability of the system within 50 cycles is verified. These findings demonstrate a new strategy to innovate MEA absorbents currently widely used in commercial post-combustion CO₂ capture plants.

Facile Fabrication of Monodispersed Carbon Sphere: A Pathway Toward Energy-Efficient Direct Air Capture (DAC) Using Amino Acids

Direct removal of carbon dioxide (CO₂ ) from the atmosphere, known as direct air capture (DAC) is attracting worldwide attention as a negative emission technology to control atmospheric CO₂ concentrations. However, the energy-intensive nature of CO₂ absorption-desorption processes has restricted deployment of DAC operations. Catalytic solvent regeneration is an effective solution to tackle this issue by accelerating CO₂ desorption at lower regeneration temperatures. This work reports a one-step synthesis methodology to prepare monodispersed carbon nanospheres (MCSs) using trisodium citrate as a structure-directing agent with acidic sites. The assembly of citrate groups on the surface of MCSs enables consistent spherical growth morphology, reduces agglomeration and enhances water dispersibility. The functionalization-assisted synthesis produces uniform, hydrophilic nanospheres of 100-600 nm range. This work also demonstrates that the prepared MCSs can be further functionalized with strong Brønsted acid sites, providing high proton donation ability. Furthermore, the materials can be effectively used in a wide range of amino acid solutions to substantially accelerate CO₂ desorption (25.6% for potassium glycinate and 41.1% for potassium lysinate) in the DAC process. Considering the facile synthesis of acidic MCSs and their superior catalytic efficiency, these findings are expected to pave a new path for energy-efficient DAC.

Single atom solutions for carbon dioxide capture

New solvents are considered to be one of the effective methods to facilitate the reaction rate and lower the reaction energy barrier. However, the common method to develop a new solvent has come to a dead end. Thus, a single atom in solvent to produce a single atom solution is designed to create the breakthrough. Eight kinds of single atom solutions are prepared as new absorbents. Experiments prove the single atom in the solutions and their charge-producing effects. A density functional theory model is developed to analyze the microscale characteristics. Meanwhile, it has been applied in carbon dioxide capture. The CO₂ desorption rate is intensified in the single atom solution system due to the controlled reaction energy barrier. The results show that single atom solutions produce a maximum voltage of 2.12 V and, thus, contribute to near zero energy consumption by effectively harvesting the substantial waste heat below 373 K.

Process coupling of CO2 reduction and 5-HMF oxidation mediated by defect-enriched layered double hydroxides

Aiming at the comprehensive utilization of waste carbon resources and renewable carbon resources, we put forward the photocatalytic coupling process of CO₂ reduction and 5-hydroxymethylfurfural (5-HMF) oxidation mediated by the anionic compound of layered double hydroxides (LDHs). Specifically, a ZnNiFe-LDH was synthesized by co-precipitation method, during which CO₂ was stored between LDH layers in the form of carbonate. Then, a certain amount of metal vacancies were introduced into LDH nanosheets by selectively etching Zn²⁺ ions. ICP-AES, EPR and XPS showed that the concentration of Zn vacancies gradually increased with the etching time prolonging, which thus optimized the electronic structure of LDH layers. Under the catalysis of the electron-rich metal cations and hydroxyl groups on the layers, the interlayer carbonate was in situ reduced into CO coupled accompanied with the 5-HMF oxidation to 2.5-furandiformaldehyde (DFF). Compared with the unetched ZnNiFe-LDHs, the CO and DFF yields over the LDHs etched for 3 h were increased by 2.84 and 2.82 times under UV-vis irradiation with a density of 500 mW cm^-2. Finally, combined with isotope-labeled ¹³CO₂ experiments and in situ FTIR characterization, we revealed the possible coupling mechanism and defect-induced performance enhancement mechanism.

[EMmim][NTf2 ]-a Novel Ionic Liquid (IL) in Catalytic CO2 Capture and ILs' Applications

Ionic liquids (ILs) have been used for carbon dioxide (CO₂ ) capture, however, which have never been used as catalysts to accelerate CO₂ capture. The record is broken by a uniquely designed IL, [EMmim][NTf₂ ]. The IL can universally catalyze both CO₂ sorption and desorption of all the chemisorption-based technologies. As demonstrated in monoethanolamine (MEA) based CO₂ capture, even with the addition of only 2000 ppm IL catalyst, the rate of CO₂ desorption-the key to reducing the overall CO₂ capture energy consumption or breaking the bottleneck of the state-of-the-art technologies and Paris Agreement implementation-can be increased by 791% at 85 °C, which makes use of low-temperature waste heat and avoids secondary pollution during CO₂ capture feasible. Furthermore, the catalytic CO₂ capture mechanism is experimentally and theoretically revealed.

MOF-Derived Robust and Synergetic Acid Sites Inducing C-N Bond Disruption for Energy-Efficient CO2 Desorption

Amine-based scrubbing technique is recognized as a promising method of capturing CO₂ to alleviate climate change. However, the less stability and poor acidity of solid acid catalysts (SACs) limit their potential to further improve amine regeneration activity and reduce the energy penalty. To address these challenges, here, we introduce two-dimensional (2D) cobalt-nitrogen-doped carbon nanoflakes (Co-N-C NSs) driven by a layered metal-organic framework that work as SACs. The designed 2D Co-N-C SACs can exhibit promising stability, superhydrophilic surface, and acidity. Such 2D structure also contains well-confined Co-N₄ Lewis acid sites and -OH Brønsted acid sites to have a synergetic effect on C-N bond disruption and significantly increase CO₂ desorption rate by 281% and reduce the reaction temperatures to 88 °C, minimizing water evaporation by 20.3% and subsequent regeneration energy penalty by 71.7% compared to the noncatalysis.

Metal Oxyhydroxide Catalysts Promoted CO2 Absorption and Desorption in Amine-Based Carbon Capture: A Feasibility Study

The huge energy penalty of CO₂ desorption is the greatest challenge impeding the commercial application of amine-based CO₂ capture. To deal with this problem, a series of metal oxide and oxyhydroxide catalysts were synthesized in this study to kinetically facilitate the CO₂ desorption from 5.0 M monoethanolamine (MEA). The effects of selected catalysts on CO₂ absorption kinetics, CO₂ absorption capacity, CO₂ reaction enthalpy, and desorption duty reduction of 2.0 M MEA were investigated by a true heat flow reaction calorimeter to access the practical feasibility of the catalytic CO₂ desorption. The kinetic study of catalytic CO₂ desorption was also carried out. CO₂ desorption chemistry, catalyst characterization, and structure-function relationships were investigated to reveal the underlying mechanisms. Results show that addition of the catalyst had slight effects on the CO₂ absorption kinetics and CO₂ reaction enthalpy of MEA. In contrast, the CO₂ desorption efficiency greatly increased from 28% in reference MEA to 52% in ZrO(OH)₂-aided MEA. Compared to the benchmark catalyst HZSM-5, ZrO(OH)₂ exhibited a 13% improvement in CO₂ desorption efficiency. More importantly, compared to the reference MEA, the CO₂ desorption duties of ZrO(OH)₂ and FeOOH-aided MEA significantly reduced by 45 and 47% respectively, which are better than those of most other reported catalysts. The large surface area, pore volume, pore diameter, and amount of surface hydroxyl groups of ZrO(OH)₂ and FeOOH afforded the catalytic performance by promoting the adsorption of alkaline speciation (e.g., MEA and HCO₃ ^-) onto the particle surface.

Chemical looping based ammonia production-A promising pathway for production of the noncarbon fuel

Ammonia, primarily made with Haber-Bosch process developed in 1909 and winning two Nobel prizes, is a promising noncarbon fuel for preventing global warming of 1.5 °C above pre-industrial levels. However, the undesired characteristics of the process, including high carbon footprint, necessitate alternative ammonia synthesis methods, and among them is chemical looping ammonia production (CLAP) that uses nitrogen carrier materials and operates at atmospheric pressure with high product selectivity and energy efficiency. To date, neither a systematic review nor a perspective in nitrogen carriers and CLAP has been reported in the critical area. Thus, this work not only assesses the previous results of CLAP but also provides perspectives towards the future of CLAP. It classifies, characterizes, and holistically analyzes the fundamentally different CLAP pathways and discusses the ways of further improving the CLAP performance with the assistance of plasma technology and artificial intelligence (AI).

Nanolayer-Constructed TiO(OH)2 Microstructures for the Efficiently Selective Removal of Cationic Dyes via an Electrostatic Interaction and Adsorption Mechanism

Efficient removal of organic dyes from contaminated water has become a great challenge and urgent work due to increasingly serious environmental problems. Here, we have for the first time prepared nanolayer-constructed TiO(OH)₂ microstructures which can present negative charge by deprotonation of the hydroxyl group to efficiently and selectively remove cationic dyes from aqueous solution through electrostatic interaction and an attraction mechanism. The nanolayer-constructed TiO(OH)₂ microstructures achieve a high adsorption capacity of 257 mg g^-1 for methylene blue (MB). The adsorption kinetics, thermodynamics, and isotherms of MB over the TiO(OH)₂ microstructures have been studied systemically. The experimental measurements and corresponding analyses demonstrate that the adsorption process of MB on TiO(OH)₂ microstructures follows a kinetic model of pseudo-second-order adsorption, agrees well with the Langmuir isotherm mode, and is a spontaneous and exothermic physisorption. Fourier transform infrared (FT-IR) spectra confirm that the prepared TiO(OH)₂ microstructures possess hydroxyl group which can deprotonate to present negative charge in solution. Further experimental studies evidently demonstrate that the TiO(OH)₂ microstructures also can remove other cationic dyes with positive charge such as basic yellow 1, basic green 4, and crystal violet but cannot adsorb anionic dye of methyl orange (MO) with negative charge in aqueous solution. The measurements for FT-IR spectra and the adsorption of cationic and anionic dyes evidently reveal that the adsorption of cationic dyes over the TiO(OH)₂ microstructures is achieved by the electrostatic interaction and attraction between TiO(OH)₂ and the dye. This work opens a strategy for the design of new absorbents to efficiently remove organic dyes from aqueous solution through an electrostatic attraction-driven adsorption process.

A Review on Enhancing Solvent Regeneration in CO2 Absorption Process Using Nanoparticles

The employment of nanoparticles in solvents is a promising method to reduce the energy consumption during solvent regeneration. Numerous experimental and theoretical studies have been conducted to investigate the remarkable enhancement of nanoparticles. Yet, there are limited reviews on the mechanistic role of nanoparticles in enhancing the solvent regeneration performance. This review addresses the recent development on the employment of various nanoparticles, which include metals oxides, zeolites and mesoporous silicas, to enhance the mass and heat transfer, which subsequently minimize the solvent regeneration energy. The enhancement mechanisms of the nanoparticles are elaborated based on their physical and chemical effects, with a comprehensive comparison on each nanoparticle along with its enhancement ratio. This review also provides the criteria for selecting or synthesizing nanoparticles that can provide a high regeneration enhancement ratio. Furthermore, the future research prospects for the employment of nanoparticles in solvent regeneration are also recommended.

Engineered assembly of water-dispersible nanocatalysts enables low-cost and green CO2 capture

Catalytic solvent regeneration has attracted broad interest owing to its potential to reduce energy consumption in CO₂ separation, enabling industry to achieve emission reduction targets of the Paris Climate Accord. Despite recent advances, the development of engineered acidic nanocatalysts with unique characteristics remains a challenge. Herein, we establish a strategy to tailor the physicochemical properties of metal-organic frameworks (MOFs) for the synthesis of water-dispersible core-shell nanocatalysts with ease of use. We demonstrate that functionalized nanoclusters (Fe₃O₄-COOH) effectively induce missing-linker deficiencies and fabricate mesoporosity during the self-assembly of MOFs. Superacid sites are created by introducing chelating sulfates on the uncoordinated metal clusters, providing high proton donation capability. The obtained nanomaterials drastically reduce the energy consumption of CO₂ capture by 44.7% using only 0.1 wt.% nanocatalyst, which is a ∽10-fold improvement in efficiency compared to heterogeneous catalysts. This research represents a new avenue for the next generation of advanced nanomaterials in catalytic solvent regeneration.

Catalytic solvent regeneration is of interest to reduce energy consumption in CO2 separation, however, the development of engineered nanocatalysts remains a challenge. Here, a new avenue is presented for the next generation of advanced metal-organic frameworks (MOFs) in energy-efficient CO2 capture.

Water-Dispersible Nanocatalysts with Engineered Structures: The New Generation of Nanomaterials for Energy-Efficient CO2 Capture

The high energy demand of CO₂ absorption-desorption technologies has significantly inhibited their industrial utilization and implementation of the Paris Climate Accord. Catalytic solvent regeneration is of considerable interest due to its low operating temperature and high energy efficiency. Of the catalysts available, heterogeneous catalysts have exhibited relatively poor performances and are hindered by other challenges, which have slowed their large-scale deployment. Herein, we report a facile and eco-friendly approach for synthesizing water-dispersible Fe₃O₄ nanocatalysts coated with a wide range of amino acids (12 representative molecules) in aqueous media. The acidic properties of water-dispersible nanocatalysts can be easily tuned by introducing different functional groups during the hydrothermal synthesis procedure. We demonstrate that the prepared nanocatalysts can be used in energy-efficient CO₂ capture plants with ease-of-use, at very low concentrations (0.1 wt %) and with extra-high efficiencies (up to ∼75% energy reductions). They can be applied in a range of solutions, including amino acids (i.e., short-chain, long-chain, and cyclic) and amines (i.e., primary, tertiary, and primary-tertiary mixture). Considering the superiority of the presented water-dispersible nanocatalysts, this technology is expected to provide a new pathway for the development of energy-efficient CO₂ capture technologies.

Highly Efficient Electrocatalytic CO2 Reduction to C2+ Products on a Poly(ionic liquid)-Based Cu(0)-Cu(I) Tandem Catalyst

Electroreduction of CO 2 on polymer-modified Cu-based catalyst has shown high multi-electron reduction (> 2e - ) selectivity, while most of the corresponding current densities are still too small to support industrial applications. In this work, we designed a poly(ionic liquid) (PIL)-based Cu(0)-Cu(I) tandem catalyst for producing C 2+ products with both high reaction rate and high selectivity. Remarkably, a high C 2+ faradaic efficiency (FE C2+ ) of 76.1% with a high partial current density of 304.2 mA cm -2 is obtained. Mechanistic studies reveal the numbers and highly dispersed Cu(0)-PIL-Cu(I) interfaces are vital for such a reactivity. Specifically, Cu nanoparticles derived Cu(0)-PIL interfaces account for high current density and a moderate C 2+ selectivity, while Cu(I) species derived PIL-Cu(I) interfaces exhibit high activity of C-C coupling with the local enriched *CO intermediate. Besides, the presence of PIL layer promotes the C 2+ selectivity by lowering the barrier of C-C coupling.

TiO2 Coating Strategy for Robust Catalysis of the Metal-Organic Framework toward Energy-Efficient CO2 Capture

High energy duty restricts the application of amine-based absorption in CO2 capture and limits the achievement of carbon neutrality. Although regenerating the amine solvent with solid acid catalysts can increase energy efficiency, inactivation of the catalyst must be addressed. Here, we report a robust metal-organic framework (MOF)-derived hybrid solid acid catalyst (SO42-/ZIF-67-C@TiO2) with improved acidity for promoting amine regeneration. The TiO2 coating effectively prevented the active components stripping from the surface of the catalyst, thus prolonging its lifespan. The well-protected Co-Nx sites and protonated groups introduced onto the TiO2 surface increased the amount and rate of CO2 desorption by more than 64.5 and 153%, respectively. Consequently, the energy consumption decreased by approximately 36%. The catalyzed N-C bond rupture and proton transfer mechanisms are proposed. This work provides an effective protection strategy for robust acid catalysts, thus advancing the CO2 capture with less energy duty.

One-Step Synthesized SO42-/ZrO2-HZSM-5 Solid Acid Catalyst for Carbamate Decomposition in CO2 Capture

Amine-based CO₂ capture technology requires high-energy consumption because the desorption temperature required for carbamate breakdown during absorbent regeneration is higher than 110 °C. In this study, we report a stable solid acid catalyst, namely, SO₄^2-/ZrO₂-HZSM-5 (SZ@H), which has improved Lewis acid sites (LASs) and Bronsted acid sites (BASs). The improved LASs and BASs enabled the CO₂ desorption temperature to be decreased to less than 98 °C. The BASs and LASs of SZ@H preferred to donate or accept protons; thus, the amount and rate of CO₂ desorption from spent monoethanolamine were more than 40 and 37% higher, respectively, when using SZ@H than when not using any catalyst. Consequently, the energy consumption was reduced by approximately 31%. A catalyzed proton-transfer mechanism is proposed for SZ@H-catalyzed CO₂ regeneration through experimental characterization and theoretical calculations. The results reveal the role of proton transfer during CO₂ desorption, which enables the feasibility of catalysts for CO₂ capture in industrial applications.

Improving the Reliability and Accuracy of Ammonia Quantification in Electro- and Photochemical Synthesis

The reliable and accurate quantification of ammonia in electrochemical and photochemical experiments has been a technical challenge owing to the extremely low concentration of generated ammonia, interference from trace amounts of cations and organic compounds, and ammonia contamination from various sources. As a result, overestimation and significant errors may happen in many research works. Herein, accuracy and precision of ion chromatography (IC) are evaluated at different pH; excellent performance with a low detection limit (<2 μg L^-1 ) under acidic and neutral conditions is found, whereas the linearity is unsatisfactory in the low NH₄ ⁺ concentration range (0-100 μg L^-1 ) under alkaline conditions. High concentrations of Li⁺ and Na⁺ are difficult to separate from NH₄ ⁺ in conventional IC, but this can be solved by employing a high-exchange-capacity column or gradient elution. The interference effects of 14 common transition metal cations and 6 common organic compounds on the quantification of ammonium with low-level concentration (500 μg L^-1 ) using IC are systematically investigated, and the results demonstrate good robustness. The overestimation caused by ammonia contamination from reagent water, surroundings, and even the analytical grade of inorganic and organic reagents are confirmed and the results indicate the necessity to prepare and test fresh electrolyte solutions before each experiment, owing to the high sensitivity of acidic and neutral solutions to ammonia contamination from the surroundings. The ammonization of a Nafion membrane during experiments and the underestimation in quantification are also discussed. Finally, a reliable level of synthesized ammonia is identified and some recommendations are presented to improve the reliability and accuracy of ammonia quantification.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

CO2 hydrogenation to high-value products via heterogeneous catalysis

Recently, carbon dioxide capture and conversion, along with hydrogen from renewable resources, provide an alternative approach to synthesis of useful fuels and chemicals. People are increasingly interested in developing innovative carbon dioxide hydrogenation catalysts, and the pace of progress in this area is accelerating. Accordingly, this perspective presents current state of the art and outlook in synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols through two leading hydrogenation mechanisms: methanol reaction and Fischer-Tropsch based carbon dioxide hydrogenation. The future research directions for developing new heterogeneous catalysts with transformational technologies, including 3D printing and artificial intelligence, are provided.

Carbon dioxide (CO₂) capture and conversion provide an alternative approach to synthesis of useful fuels and chemicals. Here, Ye et al. give a comprehensive perspective on the current state of the art and outlook of CO₂ catalytic hydrogenation to the synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols.

Review of liquid nano-absorbents for enhanced CO2 capture

Liquid nano-absorbents have become a topic of interest as a result of their enhanced mass-transfer performance for CO₂ capture. They are believed to have revolutionized the conventional CO₂ chemisorption process by largely improving CO₂ capture kinetics and reducing the energy requirement for solvent regeneration. Two classes of nanomaterial-based CO₂ capture absorbents, amine-based nanoparticle suspensions (nanofluids) and nanoparticle organic hybrid materials (NOHMs), have been developed, with significant progress achieved in recent decades. This review addresses two key questions for these two state-of-the-art nanomaterials: how are the physical and chemical properties of the prepared liquid nano-absorbents transformed relative to those of the base fluids? And how does the transformation of the properties affect the CO₂ capture behavior? While the current synthesis procedure for liquid nano-absorbents is quite straightforward, more advanced synthesis methods for long-term nanoparticle stability have been suggested for the future. Nanofluids have been shown to increase the CO₂ uptake by over 20% and the CO₂ capture rate by 2-93% compared with the values observed with neat amine solvents. Nanoparticles with catalytic effects on CO₂ capture can significantly increase the CO₂ desorption rate by as high as 4000%. NOHMs exhibit the interesting feature of enhanced mass transfer in CO₂ capture because of the unique pathway network that is created in them for CO₂ to reach specific functional groups. NOHMs promise an effect of combined CO₂ capture and conversion, and can be used especially as electrolytes for CO₂ electro-reduction. However, there are still some challenges for the application of these materials in real life, such as poor stability and high viscosity. Therefore, efficient CO₂ capture processes using these solvents need to be urgently developed and studied in the future.

CO2 Decomposition in CO2 and CO2 /H2 Spark-like Plasma Discharges at Atmospheric Pressure

In this work, a spark-like plasma discharge is ignited in pure CO₂ and in CO₂ /H₂ mixtures to investigate CO formation. Power pulsing is used to limit arc formation to sustain a high current transient "spark-like" plasma consisting of a mixed mode discharge comprising an initial current pulse ("spark") followed by a longer-lived glow mode thorough each half cycle of the applied voltage. In pure CO₂ , the efficiency ranged between 20-50 % for CO₂ conversions between 9-18 % for gas residence times of 100-600 ms. Adding H₂ as a co-reactant was investigated for a wide range of mixture ratios. The outlet gas was found to produce O₂ -free mixtures of CO/H₂ /CO₂ . Conversion rates in CO₂ /H₂ mixtures are found to be similar to pure CO₂ at equivalent residence times. The primary role of H₂ as a co-reactant is therefore found to be the removal of O₂ formed during dissociation of CO₂ . The energy cost of this dilution resulted in reduced efficiency for CO₂ conversion (from 41 to 18 %), which is correlated to the efficiency drop found for pure CO₂ conversion at lower flows. Opportunities for optimising this small volume "unit-cell" spark reactor are encouraged by the results presented. This approach could enable deployment of serial or parallel combinations of such reactors capable of dealing cost-effectively with the conversion of the larger CO₂ and CO₂ /H₂ volumes required in future industry applications.

Application of the Thermodynamic Cycle to Assess the Energy Efficiency of Amine-Based Absorption of Carbon Capture

The thermodynamic cycle, as a significant tool derived from equilibrium, could provide a reasonable and rapid energy profile of complicated energy systems. Such a function could strongly promote an in-depth and direct understanding of the energy conversion mechanism of cutting-edge industrial systems, e.g., carbon capture system (CCS) However, such applications of thermodynamics theory have not been widely accepted in the carbon capture sector, which may be one of the reasons why intensive energy consumption still obstructs large-scale commercialization of CCS. In this paper, a kind of thermodynamic cycle was developed as a tool to estimate the lowest regeneration heat (Qre) of a benchmark solvent (MEA) under typical conditions. Moreover, COPCO2, a new assessment indicator, was proposed firstly for energy-efficiency performance analysis of such a kind of CCS system. In addition to regeneration heat and second-law efficiency (η2nd), the developed COPCO2 was also integrated into the existing performance analysis framework, to assess the energy efficiency of an amine-based absorption system. Through variable parameter analysis, the higher CO2 concentration of the flue gas, the higher COPCO2, up to 2.80 in 16 vt% and the Qre was 2.82 GJ/t, when Rdes = 1 and ΔTheat-ex = 10 K. The η2nd was no more than 30% and decreased with the rise of the desorption temperature, which indicates the great potential of improvements of the energy efficiency.

A new and different insight into the promotion mechanisms of Ga for the hydrogenation of carbon dioxide to methanol over a Ga-doped Ni(211) bimetallic catalyst

The hydrogenation of CO₂ to CH₃OH is one of the most promising technologies for the utilization of captured CO₂ in the future. Nano Ni-Ga bimetallic catalysts have been proven to be excellent catalysts in the hydrogenation of CO₂ to CH₃OH. To investigate the promotion mechanisms of Ga for the hydrogenation of CO₂ to CH₃OH over Ga-doped Ni catalysts and the wide application of these promotion mechanisms in other catalysts and reactions, herein, density functional theory (DFT) was employed. The reaction mechanisms and the properties of Ni(211) and Ga-Ni(211) surfaces were comparatively studied. The results show that the Ni sites on both the Ni(211) and the Ga-Ni(211) surfaces are active sites, and the most stable structures of the intermediates are similar. Moreover, the Ga-Ni(211) surface is more favorable for the hydrogenation of CO₂, whereas Ni(211) is more favorable for the dissociation of CO₂. The activation barrier of the rate-limiting step in the CH₃OH formation pathway on Ni(211) is 0.54 eV higher than that on Ga-Ni(211). According to the analyses of the projected density of states (PDOS) and Hirshfeld charge transfer, the addition of Ga atoms demonstrates the reactivity of the Ga-doped Ni(211) surfaces. Most importantly, the replacement of some secondary active sites of Ni atoms with the non-active Ga atoms may lower the activities of the secondary active sites and strengthen the activities of the active sites at the step edge. These results provide a new perspective for the reaction mechanism of the hydrogenation of CO₂ to CH₃OH over the state-of-the-art Ga-doped catalysts.