Hydroxide Based Integrated CO2 Capture from Air and Conversion to Methanol

Nanosilica polyamidoamine dendrimers for enhanced direct air CO2 capture

Exploring efficient systems to recover CO2 from the atmosphere could be a way to address the global carbon emissions issue. Herein, we report the synthesis of nanosilica (NS) functionalized with polyamidoamine (PAMAM) dendrimers (NS-PAMAM) as efficient adsorbents for CO2 capture under simulated direct air capture (DAC) (400 ppm CO2 in helium at 30 °C) and indoor air (≥400 ppm, 50 ± 3% RH at 30 °C) conditions. The results inferred that the 1st (NS-G1.0), 2nd (NS-G2.0), 3rd (NS-G3.0), and 4th (NS-G4.0) generations of the NS-PAMAM dendrimers exhibited excellent performance for CO2 capture. Compared to the other generations, NS-G3.0 demonstrated superior CO2 adsorption capacities of 0.50 mmol g-1 under simulated dry CO2 conditions (400 ppm in He), 1.02 mmol g-1 under indoor air (dry) CO2 conditions (≥400 ppm, 26 ± 3% RH), and 1.54 mmol g-1 under indoor air (humid) CO2 conditions (≥400 ppm, 50 ± 3% RH). The study included the evaluation of CO2 adsorption-desorption performance of the NS-PAMAM dendrimers under varying structural and chemical parameters, kinetics, regeneration at low temperature (80 °C), as well as CO2 adsorption under humid conditions. Additionally, NS-G3.0 displayed a substantially superior performance with stable CO2 capture displayed during ten short temperature swing adsorption (TSA) cycles, making it a promising candidate for CO2 capture from ambient air. Finally, we demonstrated the recovery and reutilization of the captured CO2 for both the synthesis of formate via carbonate hydrogenation and for the production of calcium carbonate pellets.

Ionic Lignin Polymers for Controlled CO2 Capture, Release, and Conversion into High-Value Chemicals

In this study, an innovative and cost-effective ionic polymer for CO2 capture and utilization for the first time, using abundant and nonfood-based biomass lignin is reported. The modified ionic polymer synthesizes through the reaction of glycidyltrimethylammonium chloride with lignin under alkaline conditions to yield quaternary ammonium ionic functionality. Subsequently, the hydroxide-based pure ionic lignin polymer is employed for CO2 capture from both direct air and concentrated CO2 sources at room temperature and atmospheric pressure. Structural characterization of the polymers is accomplished through 1H, 13C, and 2D-heteronuclear single quantum coherence (HSQC) NMR, and FT-IR spectroscopy. The CO2 capture process is established through the formation of bicarbonate ions alongside the presence of CO2. The captured CO2 is precisely quantified by using inverse-gated proton decoupled 13C NMR with an internal standard (trioxane). Remarkably, the captured-CO2 amounts of ionic lignin polymer are 1.06 mmol g-1 (47 mg g-1) from concentrated-CO2 source and 0.60 mmol g-1 (26 mg g-1) from direct-air. The captured-CO2 in ionic lignin polymer is released in controlled manner and utilized in the synthesis of cyclic carbonate, showcasing the productive application of the captured carbon. Moreover, the fully controlled recovering of ionic lignin polymer achieves via repeated CO2 release ↔ CO2 capture.

Converting CO2 Into Natural Gas Within the Autoclave: A Kinetic Study on Hydrogenation of Carbonates in Aqueous Solution

Catalytic conversion of carbon dioxide (CO2) into value-added chemicals is of pivotal importance, well the cost of capturing CO2 from dilute atmosphere is super challenge. One promising strategy is combining the adsorption and transformation at one step, such as applying alkali solution that could selectively reduce carbonate (CO3 2-) as consequences of CO2 adsorption. Due to complexity of this system, the mechanistic details on controlling the hydrogenation have not been investigated in depth. Herein, Ru/TiO2 catalyst was applied as a probe to elucidate the mechanism of CO3 2- activation, in which with thermodynamic and kinetic investigations, a compact Langmuir-Hinshelwood reaction model was established which suggests that the overall rate of CO3 2- hydrogenation was controlled by a specific C-O bond rupture elementary step within HCOO- and the Ru surface was mainly covered by CO3 2- or HCOO- at independent conditions. This assumption was further supported by negligible kinetic isotope effects (kH/kD≈1), similarity on reaction barriers of CO3 2- and HCOO- hydrogenation (ΔH≠ hydr,Na2CO3 and ΔH≠ hydr,HCOONa) and a non-variation of entropy (ΔS≠ hydr≈0). More interestingly, the alkalinity of the solution is certainly like a two sides in a sword and could facilitate the adsorption of CO2 while hold back catalysis during CO3 2- hydrogenation.

Quaternized Graphene for High-Performance Moisture Swing Direct Air Capture of CO2

Nowadays, moisture-swing adsorption technology still relies on quaternary ammonium resins with limited CO2 capacity under ambient air conditions. In this work, a groundbreaking moisture-driven sorbent is developed starting from commercial graphene flakes and using glycidyltrimethylammonium chloride for incorporation of CO2-sensitive quaternary ammonium functional groups. Boasting an outstanding CO2 capture performance under ultra-diluted conditions (namely, 3.24 mmol g-1 at CO2 400 ppm and 20% RH), the functionalized sorbent (fGO) features clear competitive advantages over current technologies for direct air capture. Notably, fGO demonstrated unprecedented moisture-swing capacity, ease of regenerability, versatility, selectivity, and longevity. These distinctive features position the fGO as an advanced and promising solution, showcasing its potential to outperform existing methods for moisture-swing direct air capture of CO2.

Addition of Imidazolium-Based Ionic Liquid to Improve Methanol Production in Polyamine-Assisted CO2 Capture and Conversion Systems Using Pincer Catalysts

Ionic liquids have been studied as CO2 capture agents. However, they are rarely used in combined CO2 capture and conversion processes. Utilizing imidazolium-based ionic liquids, the conversion of CO2 to methanol was greatly improved in polyamine assisted systems catalyzed by homogeneous pincer catalysts with Ru and Mn metal centers. Among the ionic liquids tested, [BMIM]OAc was found to perform the best under the given reaction conditions. Among the polyamine tested, pentaethylenehexamine (PEHA) led to the highest conversion rates. Ru-Macho and Ru-Macho-BH were the most active catalysts. Direct air capture utilizing PEHA as the capture material was also demonstrated and produced an 86 % conversion of the captured CO2 to methanol in the presence of [BMIM]OAc.

Biomimetic Frustrated Lewis Pair Catalysts for Hydrogenation of CO to Methanol at Low Temperatures

The industrial production of methanol through CO hydrogenation using the Cu/ZnO/Al2O3 catalyst requires harsh conditions, and the development of new catalysts with low operating temperatures is highly desirable. In this study, organic biomimetic FLP catalysts with good tolerance to CO poison are theoretically designed. The base-free catalytic reaction contains the 1,1-addition of CO into a formic acid intermediate and the hydrogenation of the formic acid intermediate into methanol. Low-energy spans (25.6, 22.1, and 20.6 kcal/mol) are achieved, indicating that CO can be hydrogenated into methanol at low temperatures. The new extended aromatization-dearomatization effect involving multiple rings is proposed to effectively facilitate the rate-determining CO 1,1-addition step, and a new CO activation model is proposed for organic catalysts.

Unraveling the role of internal-external metal substitution in Zn3[Co(CN6)]2 for the styrene oxide-CO2 cycloaddition reaction

We investigated the influence of the structural and textural properties along with the chemical environment of pure Zn3[Co(CN)6]2 in comparison with the modified phases on the catalytic performance in the cycloaddition reaction between styrene oxide and CO2. We relate these to the proposed reaction pathways and mechanisms. The natural cubic phase (ZnCoCn) was dehydrated to obtain the rhombohedral phase (ZnCoRn), while the stabilized cubic phase (ZnCoCs) was synthesized by substituting external zinc atoms with cadmium atoms. The rhombohedral stabilized phase (ZnCoRs) was achieved by the internal cobalt change with iron. All the materials were extensively characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), and N2 adsorption. The catalytic behavior of the four phases was tested. The crystalline structure of each phase was obtained, and by XPS, it was demonstrated that the chemical environments of all elements conforming to the rhombohedral stabilized phase are different from those of all other materials owing to the exchange of internal metals. The bulk textural properties were similar; only the ZnCoRs presented more micropore area but did not exceed the total surface area of the other materials. The product distribution and yield at reaction times of 2 h and 6 h were closer to those of the cubic phases. The natural rhombohedral phase exhibits the best performance. The tetrabutylammonium bromide (TBAB) and rhombohedral stabilized phase work together to yield a bigger copolymer quantity at the expense of the styrene carbonate (StCO3) production. From the proposed mechanism, the TBAB cation (TBA+) has a "protection" function that drives the closing of the StCO3 ring; however, the charge distribution anisotropy in the four nitrogen atoms generated by Co replacement in ZnCoRs could hold TBA+ as the reaction time progressed, causing an unavailability that triggered the copolymerization propagation step.

Integrated Carbon Dioxide Capture and Conversion to Methanol Utilizing Tertiary Amines over a Heterogenous Cu/ZnO/Al2O3 Catalyst

Increasing carbon dioxide emissions has sparked a growing interest in capturing these emissions at the source of their release. For such processes, amines can be used as carbon dioxide capture agents. Herein, CO2 was captured under ambient conditions using solutions of amines and polyamines in ethylene glycol. The captured solutions were then successfully hydrogenated to methanol under hydrogen pressure with a heterogeneous Cu/ZnO/Al2O3 industrial catalyst. An extensive amine scope found that tetramethyl-1,6-hexanediamine, with two tertiary amine sites, provided the highest methanol productivity. This reaction was then optimized to achieve up to 89% methanol yield under relatively mild conditions of 250 °C and 80 bar H2 pressure. The catalyst was shown to be recyclable over five reaction cycles.

Reactivity of NHI-Stabilized Heavier Tetrylenes towards CO2 and N2 O

A heteroleptic amino(imino)stannylene (TMS2 N)(It BuN)Sn: (TMS=trimethylsilyl, It Bu=C[(N-t Bu)CH]2 ) as well as two homoleptic NHI-stabilized tetrylenes, (It BuN)2 E: (NHI=N-heterocyclic imine, E=Ge, Sn) are presented. VT-NMR investigations of (It BuN)2 Sn: (2) reveal an equilibrium between the monomeric stannylene at room temperature and the dimeric form at -80 °C as well as in the solid state. Upon reaction of the homoleptic tetrylenes with CO2 , both compounds insert two equivalents of CO2 , however differing bonding modes can be observed. (It BuN)2 Sn: (2) inserts one equivalent of CO2 into each Sn-N bond, giving carbamato groups coordinated κ2 O,O' to the metal center. With (It BuN)2 Ge: (3), the Ge-N bonds stay intact upon activation, being bridged by one molecule of CO2 respectively, forming 4-membered rings. Furthermore, the reactivity of 2 towards N2 O was investigated, resulting in partial oxidation to form stannylene dimer [((It BuN)3 SnO)(It BuN)Sn:]2 (6).

Expanding the Library of Ions for Moisture-Swing Carbon Capture

Developing materials that can more efficiently and cheaply capture carbon dioxide from ambient atmospheric conditions is essential for improving negative emission technologies. This study builds on the promising moisture-swing modality for direct air capture of carbon dioxide by investigating the use of several new anions─orthosilicate, borate, pyrophosphate, tripolyphosphate, and dibasic phosphate─that when introduced into ion-exchange resins allow for the cyclable capture of CO2 under dry conditions and its release under wet conditions. These ions, as well as many others that failed to show moisture-swing performance, are tested and directly compared thermodynamically and kinetically to understand their differences. This includes the use of analytical approaches new to the carbon capture field, such as the correlation of adsorption isotherms to moisture-swing performance, the use of phase lag kinetics, the examination of the humidity-carbon capture hysteresis of the sorbents, and the precise quantification of ion loading using inductively coupled plasma-optical emission spectroscopy. Phosphate dibasic was found to have the largest mass-normalized CO2 moisture-swing capacity, whereas phosphate tribasic had the best performance when factoring in kinetics, and pyrophosphate had the highest swing capacity when normalizing on a per-ion or per-unit-charge basis. This work not only sheds light on ways to improve DAC but also provides insights pertinent to the advancement of gas separation, negative emission technologies, and sorbent materials.

Engineering the activity and stability of ZIF-8(Zn/Co)@g-C3N4 nanocomposites and their synergistic action in converting atmospheric CO2 into cyclic carbonates

The development of novel catalytic materials that integrate multifunctional sites has significant implications for expanding the utilization of CO2 resources. However, simultaneously achieving high activity and stability remains a formidable challenge. In this study, a series of ZIF-8(Zn/Co)@g-C3N4 nanocomposites were prepared by employing a thermo-physical compounding strategy that involved the combination of nitrogen-rich graphitic carbon nitride (g-C3N4) nanosheets with ZIF-8(ZnCo). The influences of different compositions of g-C3N4 and ZIF-8(Zn/Co) on the catalyst structure were systematically investigated. Subsequently, the catalytic activities of these nanocomposites towards the cycloaddition reaction between CO2 and epoxide were examined under different conditions. The presence of abundant Lewis base sites in g-C3N4 facilitates CO2 activation, while multiple Lewis acid sites in ZIF-8(Zn/Co) enable efficient epoxide activation. By working synergistically with a co-catalyst, tetrabutylammonium bromide (TBAB), CO2 and epoxides can be efficiently reacted to synthesize the corresponding cyclic carbonates under mild or even atmospheric pressure conditions. The catalytic reaction conditions were optimized, and both the catalyst's recycling performance and the scope of epoxides with various substituents were investigated. The integration of g-C3N4 and ZIF-8(Zn/Co) endows the catalytic material with exceptional structural stability and remarkable catalytic activity, thereby providing a new platform for highly efficient CO2 conversion.

Direct Air Capture and Integrated Conversion of Carbon Dioxide into Cyclic Carbonates with Basic Organic Salts

Direct air capture and integrated conversion is a very attractive strategy to reduce CO₂ concentration in the atmosphere. However, the existing capturing processes are technologically challenging due to the costs of the processes and the low concentration of CO₂. The efficient valorization of the CO₂ captured could help overcome many techno-economic limitations. Here, we present a novel economical methodology for direct air capture and conversion that is able to efficiently convert CO₂ from the air into cyclic carbonates. The new approach employs commercially available basic ionic liquids, works without the need for sophisticated and expensive co-catalysts or sorbents and under mild reaction conditions. The CO₂ from atmospheric air was efficiently captured by IL solution (0.98 molCO₂/mol_IL) and, subsequently, completely converted into cyclic carbonates using epoxides or halohydrins potentially derived from biomass as substrates. A mechanism of conversion was evaluated, which helped to identify relevant reaction intermediates based on halohydrins, and consequently, a 100% selectivity was obtained using the new methodology.

Bifunctional Gas Diffusion Electrode Enables In Situ Separation and Conversion of CO2 to Ethylene from Dilute Stream

The requirement of concentrated carbon dioxide (CO₂ ) feedstock significantly limits the economic feasibility of electrochemical CO₂ reduction (eCO₂ R) which often involves multiple intermediate processes, including CO₂ capture, energy-intensive regeneration, compression, and transportation. Herein, a bifunctional gas diffusion electrode (BGDE) for separation and eCO₂ R from a low-concentration CO₂ stream is reported. The BGDE is demonstrated for the selective production of ethylene (C₂ H₄ ) by combining high-density-polyethylene-derived porous carbon (HPC) as a physisorbent with polycrystalline copper as a conversion catalyst. The BGDE shows substantial tolerance to 10 vol% CO₂ exhibiting a Faradaic efficiency of ≈45% toward C₂ H₄ at a current density of 80 mA cm^-2 , outperforming previous reports that utilized such partial pressure (P_CO2 = 0.1 atm and above) and unaltered polycrystalline copper. Molecular dynamics simulation and mixed gas permeability assessment reveal that such selective performance is ensured by high CO₂ uptake of the microporous HPC as well as continuous desorption owing to the molecular diffusion and concentration gradient created by the binary flow of CO₂ and nitrogen (CO₂ |N₂ ) within the sorbent boundary. Based on detailed techno-economic analysis, it is concluded that this in situ process can be economically compelling by precluding the C₂ H₄ production cost associated with the energy-intensive intermediate steps of the conventional decoupled process.

Poly(ionic liquid) nanovesicles via polymerization induced self-assembly and their stabilization of Cu nanoparticles for tailored CO2 electroreduction

Herein, we report a straightforward, scalable synthetic route towards poly(ionic liquid) (PIL) homopolymer nanovesicles (NVs) with a tunable particle size of 50 to 120 nm and a shell thickness of 15 to 60 nm via one-step free radical polymerization induced self-assembly. By increasing monomer concentration for polymerization, their nanoscopic morphology can evolve from hollow NVs to dense spheres, and finally to directional worms, in which a multilamellar packing of PIL chains occurred in all samples. The transformation mechanism of NVs' internal morphology is studied in detail by coarse-grained simulations, revealing a correlation between the PIL chain length and the shell thickness of NVs. To explore their potential applications, PIL NVs with varied shell thickness are in situ functionalized with ultra-small (1 ∼ 3 nm in size) copper nanoparticles (CuNPs) and employed as electrocatalysts for CO₂ electroreduction. The composite electrocatalysts exhibit a 2.5-fold enhancement in selectivity towards C₁ products (e.g., CH₄), compared to the pristine CuNPs. This enhancement is attributed to the strong electronic interactions between the CuNPs and the surface functionalities of PIL NVs. This study casts new aspects on using nanostructured PILs as new electrocatalyst supports in CO₂ conversion to C₁ products.

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

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

Intrinsic Charge Polarization in Bi19 S27 Cl3 Nanorods Promotes Selective CC Coupling Reaction during Photoreduction of CO2 to Ethanol

Obtaining multi-carbon products via CO₂  photoreduction is a major catalytic challenge involving multielectron-mediated CC bond formation. Complex design of multicomponent interfaces that are exploited to achieve this chemical transformation, often leads to untraceable deleterious changes in the interfacial chemical environment affecting CO₂  conversion efficiency and product selectivity. Alternatively, robust metal centers having asymmetric charge distribution can effectuate CC coupling reaction through the stabilization of intermediates, for desired product selectivity. However, generating inherent charge distribution in a single component catalyst is a difficult material design challenge. Here, a novel photocatalyst, Bi₁₉ S₂₇ Cl₃ , is presented which selectively converts CO₂  to a C₂  product, ethanol, in high yield under visible light irradiation. Structural analysis through transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy reveals the presence of charge polarized bismuth centers in Bi₁₉ S₂₇ Cl₃ . The intrinsic electric field induced by charge polarized bismuth centers renders better separation efficiency of photogenerated electron-hole pair. Furthermore, charge polarized centers yield better adsorption of CO* intermediate and accelerate the rate determining CC coupling step through the formation of OCCOH intermediate. Formation of these intermediates is experimentally mapped by in situ Fourier-transform infrared spectroscopy and further confirmed by theoretical calculation.

Ceria-Supported Cobalt Catalyst for Low-Temperature Methanation at Low Partial Pressures of CO2

The direct catalytic conversion of atmospheric CO₂ to valuable chemicals is a promising solution to avert negative consequences of rising CO₂ concentration. However, heterogeneous catalysts efficient at low partial pressures of CO₂ still need to be developed. Here, we explore Co/CeO₂ as a catalyst for the methanation of diluted CO₂ streams. This material displays an excellent performance at reaction temperatures as low as 175 °C and CO₂ partial pressures as low as 0.4 mbar (the atmospheric CO₂ concentration). To gain mechanistic understanding of this unusual activity, we employed in situ X-ray photoelectron spectroscopy and operando infrared spectroscopy. The higher surface concentration and reactivity of formates and carbonyls-key reaction intermediates-explain the superior activity of Co/CeO₂ as compared to a conventional Co/SiO₂ catalyst. This work emphasizes the catalytic role of the cobalt-ceria interface and will aid in developing more efficient CO₂ hydrogenation catalysts.

Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol Economy

The traditional economy based on carbon-intensive fuels and materials has led to an exponential rise in anthropogenic CO₂ emissions. Outpacing the natural carbon cycle, atmospheric CO₂ levels increased by 50 % since the pre-industrial age and can be directly linked to global warming. Being at the core of the proposed methanol economy pioneered by the late George A. Olah, the chemical recycling of CO₂ to produce methanol, a green fuel and feedstock, is a prime channel to achieve carbon neutrality. In this direction, homogeneous catalytic systems have lately been a major focus for methanol synthesis from CO₂ , CO and their derivatives as potential low-temperature alternatives to the commercial processes. This Review provides an account of this rapidly growing field over the past decade, since its resurgence in 2011. Based on the critical assessment of the progress thus far, the present key challenges in this field have been highlighted and potential directions have been suggested for practically viable applications.

Liquid Sunshine: Formic Acid

"Liquid sunshine" is the conceptual green liquid fuel that is produced by a combination of solar energy, CO₂, and H₂O. Alcohols are commonly regarded as the preferred candidates for liquid sunshine because of their advantages of high energy density and extensive industrial applications. However, both the alcohol synthesis and H₂ release processes require harsh reaction conditions, resulting in large external energy input. Unlike alcohols, the synthesis and dehydrogenation of formic acid (FA)/formate can be performed under mild conditions. Herein, we propose liquid sunshine FA/formate as a promising supplement to alcohol. First, we outline the vision of using FA/formate as liquid sunshine and discuss its feasibility. Then, we concentrate on the application of FA/formate as liquid organic hydrogen carrier and summarize the recent developments of CO₂ hydrogenation to FA/formate and FA/formate dehydrogenation under mild conditions. Finally, we discuss the current applications, challenges, and opportunities surrounding the use of FA/formate as liquid sunshine.

Recent advances in CO2 capture and reduction

Given the continuous and excessive CO₂ emission into the atmosphere from anthropomorphic activities, there is now a growing demand for negative carbon emission technologies, which requires efficient capture and conversion of CO₂ to value-added chemicals. This review highlights recent advances in CO₂ capture and conversion chemistry and processes. It first summarizes various adsorbent materials that have been developed for CO₂ capture, including hydroxide-, amine-, and metal organic framework-based adsorbents. It then reviews recent efforts devoted to two types of CO₂ conversion reaction: thermochemical CO₂ hydrogenation and electrochemical CO₂ reduction. While thermal hydrogenation reactions are often accomplished in the presence of H₂, electrochemical reactions are realized by direct use of electricity that can be renewably generated from solar and wind power. The key to the success of these reactions is to develop efficient catalysts and to rationally engineer the catalyst-electrolyte interfaces. The review further covers recent studies in integrating CO₂ capture and conversion processes so that energy efficiency for the overall CO₂ capture and conversion can be optimized. Lastly, the review briefs some new approaches and future directions of coupling direct air capture and CO₂ conversion technologies as solutions to negative carbon emission and energy sustainability.

Recent advances in direct air capture by adsorption

Significant progress has been made in direct air capture (DAC) in recent years. Evidence suggests that the large-scale deployment of DAC by adsorption would be technically feasible for gigatons of CO₂ capture annually. However, great efforts in adsorption-based DAC technologies are still required. This review provides an exhaustive description of materials development, adsorbent shaping, in situ characterization, adsorption mechanism simulation, process design, system integration, and techno-economic analysis of adsorption-based DAC over the past five years; and in terms of adsorbent development, affordable DAC adsorbents such as amine-containing porous materials with large CO₂ adsorption capacities, fast kinetics, high selectivity, and long-term stability under ultra-low CO₂ concentration and humid conditions. It is also critically important to develop efficient DAC adsorptive processes. Research and development in structured adsorbents that operate at low-temperature with excellent CO₂ adsorption capacities and kinetics, novel gas-solid contactors with low heat and mass transfer resistances, and energy-efficient regeneration methods using heat, vacuum, and steam purge is needed to commercialize adsorption-based DAC. The synergy between DAC and carbon capture technologies for point sources can help in mitigating climate change effects in the long-term. Further investigations into DAC applications in the aviation, agriculture, energy, and chemical industries are required as well. This work benefits researchers concerned about global energy and environmental issues, and delivers perspective views for further deployment of negative-emission technologies.

Stabilizing Oxide Nanolayer via Interface Confinement and Surface Hydroxylation

Surface hydroxylation over oxide catalysts often occurs in many catalytic processes involving H₂ and H₂O, which is considered to play an important role in elementary steps of the reactions. Here, monolayer CoO and CoOH_x nanoislands on Pt(111) are used as inverse model catalysts to study the effect of surface hydroxylation on the stability of Co oxide overlayers in O₂. Surface science experiments indicate that hydroxyl groups formed on CoO nanoislands produced by deuterium-spillover can enhance oxidation resistance of the Co oxide nanostructures. Theoretical calculation shows that the interfacial adhesion between CoO and Pt is linearly strengthened with the increasing hydroxylation degree of CoO surface. Thus, the interface confinement effect between CoO and Pt can be enhanced by the surface hydroxylation due to the more reduced Co ions and stronger Co-Pt bonding at the CoOH_x/Pt interface.

Homogeneous Carbon Capture and Catalytic Hydrogenation: Toward a Chemical Hydrogen Battery System

Recent developments of CO₂ capture and subsequent catalytic hydrogenation to C1 products are discussed and evaluated in this Perspective. Such processes can become a crucial part of a more sustainable energy economy in the future. The individual steps of this catalytic carbon capture and usage (CCU) approach also provide the basis for chemical hydrogen batteries. Here, specifically the reversible CO₂/formic acid (or bicarbonate/formate salts) system is presented, and the utilized catalysts are discussed.

The role of carbon capture, utilization, and storage for economic pathways that limit global warming to below 1.5°C

The 2021 Intergovernmental Panel on Climate Change (IPCC) report, for the first time, stated that CO₂ removal will be necessary to meet our climate goals. However, there is a cost to accomplish CO₂ removal or mitigation that varies by source. Accordingly, a sensible strategy to prevent climate change begins by mitigating emission sources requiring the least energy and capital investment per ton of CO₂, such as new emitters and long-term stationary sources. The production of CO₂-derived products should also start by favoring processes that bring to market high-value products with sufficient margin to tolerate a higher cost of goods.

Model-Based Analysis for Ethylene Carbonate Hydrogenation Operation in Industrial-Type Tubular Reactors

Hydrogenation of ethylene carbonate (EC) to co-produce methanol (MeOH) and ethylene glycol (EG) offers an atomically economic route for CO2 utilization. Herein, aided with bench and pilot plant data, we established engineering a kinetics model and multiscale reactor models for heterogeneous EC hydrogenation using representative industrial-type reactors. Model-based analysis indicates that single-stage adiabatic reactors, despite a moderate temperature rise of 12 K, suffer from a narrow operational window delimited by EC condensation at lower temperatures and intense secondary EG hydrogenation at higher temperatures. Boiling water cooled multi-tubular reactors feature near-isothermal operation and exhibit better operability, especially under high pressure and low space velocity. Conduction oil-cooled reactors show U-type axial temperature profiles, rendering even wider operational windows regarding coolant temperatures than the water-cooled reactor. The revelation of operational characteristics of EC hydrogenation under industrial conditions will guide further improvement in reactor design and process optimization.

Hydrogenation of CO2 or CO2 Derivatives to Methanol under Molecular Catalysis: A Review

The atmospheric CO2 concentration has been continuously increasing due to fossil fuel combustion. The transformations of CO2 and CO2 derivatives into high value-added chemicals such as alcohols are ideal routes to mitigate greenhouse gas emissions. Among alcohol products, methanol is very promising as it fulfills the carbon neutral cycle and can be used for direct methanol fuel cells. Herein, we summarize the recent progress in the hydrogenation of CO2 or CO2 derivatives to methanol, and focus on those systems with homogeneous catalysts and molecular hydrogen as the reductant. Discussions on the catalytic systems, efficiencies, and future outlooks will be given.

The curious saga of dehydrogenation/hydrogenation for chemical hydrogen storage: a mechanistic perspective

Hydrogen storage is an indispensable component of hydrogen-based fuel economy. Chemical hydrogen storage relies on the development of lightweight compounds which can deliver high weight percentage of H₂ at moderate temperatures through dehydrogenation and can be recovered from the dehydrogenated mass by hydrogenation for reuse. In this feature article we primarily discuss the mechanistic underpinnings of the catalytic dehydrogenation of ammonia-borane, a potential candidate for hydrogen storage and the challenges associated with its regeneration from the dehydrogenated mass. Moreover, we highlight the mechanistic intricacies, viability, sustainability and unresolved issues of allied chemical hydrogen storage avenues such as the CH₃OH-CO₂ cycle.

Recent Advances of Photocatalytic Hydrogenation of CO2 to Methanol

Constantly increasing hydrocarbon fuel combustion along with high levels of carbon dioxide emissions has given rise to a global energy crisis and environmental alterations. Photocatalysis is an effective technique for addressing this energy and environmental crisis. Clean and renewable solar energy is a very favourable path for photocatalytic CO2 reduction to value-added products to tackle problems of energy and the environment. The synthesis of various products such as CH4, CH3OH, CO, EtOH, etc., has been expanded through the photocatalytic reduction of CO2. Among these products, methanol is one of the most important and highly versatile chemicals widely used in industry and in day-to-day life. This review emphasizes the recent progress of photocatalytic CO2 hydrogenation to CH3OH. In particular, Metal organic frameworks (MOFs), mixed-metal oxide, carbon, TiO2 and plasmonic-based nanomaterials are discussed for the photocatalytic reduction of CO2 to methanol. Finally, a summary and perspectives on this emerging field are provided.

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

As the world pledges to significantly cut carbon emissions, the demand for sustainable and clean energy has now become more important than ever. This includes both production and storage of energy carriers, a majority of which involve catalytic reactions. This article reviews recent developments of homogeneous catalysts in emerging applications of sustainable energy. The most important focus has been on hydrogen storage as several efficient homogeneous catalysts have been reported recently for (de)hydrogenative transformations promising to the hydrogen economy. Another direction that has been extensively covered in this review is that of the methanol economy. Homogeneous catalysts investigated for the production of methanol from CO2, CO, and HCOOH have been discussed in detail. Moreover, catalytic processes for the production of conventional fuels (higher alkanes such as diesel, wax) from biomass or lower alkanes have also been discussed. A section has also been dedicated to the production of ethylene glycol from CO and H2 using homogeneous catalysts. Well-defined transition metal complexes, in particular, pincer complexes, have been discussed in more detail due to their high activity and well-studied mechanisms.

Synthesis of mixed-valence Cu phthalocyanine/graphene/g-C3N4 ultrathin heterojunctions as efficient photocatalysts for CO2 reduction

Mixed-valence Cu phthalocyanine/graphene/g-C3N4 ultrathin heterojunctions for efficient photocatalytic CO2 reduction.

Liquid-Metal-Enabled Mechanical-Energy-Induced CO2 Conversion

A green carbon capture and conversion technology offering scalability and economic viability for mitigating CO₂ emissions is reported. The technology uses suspensions of gallium liquid metal to reduce CO₂ into carbonaceous solid products and O₂ at near room temperature. The nonpolar nature of the liquid gallium interface allows the solid products to instantaneously exfoliate, hence keeping active sites accessible. The solid co-contributor of silver-gallium rods ensures a cyclic sustainable process. The overall process relies on mechanical energy as the input, which drives nano-dimensional triboelectrochemical reactions. When a gallium/silver fluoride mix at 7:1 mass ratio is employed to create the reaction material, 92% efficiency is obtained at a remarkably low input energy of 230 kWh (excluding the energy used for dissolving CO₂ ) for the capture and conversion of a tonne of CO₂ . This green technology presents an economical solution for CO₂ emissions.

Trans Influence of Boryl Ligands in CO2 Hydrogenation on Ruthenium Complexes: Theoretical Prediction of Highly Active Catalysts for CO2 Reduction

In this work, we study the trans influence of boryl ligands and other commonly used non-boryl ligands in order to search for a more active catalyst than the ruthenium dihydride complex Ru(PNP)(CO)H2 for the hydrogenation of CO2. The theoretical calculation results show that only the B ligands exhibit a stronger trans influence than the hydride ligand and are along increasing order of trans influence as follows: –H < –BBr2 < –BCl2 ≈ –B(OCH)2 < –Bcat < –B(OCH2)2 ≈ –B(OH)2 < –Bpin < –B(NHCH2)2 < –B(OCH3)2 < –B(CH3)2 < –BH2. The computed activation free energy for the direct hydride addition to CO2 and the NBO analysis of the property of the Ru–H bond indicate that the activity of the hydride can be enhanced by the strong trans influence of the B ligands through the change in the Ru–H bond property. The function of the strong trans influence of B ligands is to decrease the d orbital component of Ru in the Ru–H bond. The design of a more active catalyst than the Ru(PNP)(CO)H2 complex is possible.

HCOOH disproportionation to MeOH promoted by molybdenum PNP complexes

Molybdenum(0) complexes with aliphatic aminophosphine pincer ligands have been prepared which are competent for the disproportionation of formic acid, thus representing the first example so far reported of non-noble metal species to catalytically promote such transformation. In general, formic acid disproportionation allows for an alternative access to methyl formate and methanol from renewable resources. MeOH selectivity up to 30% with a TON of 57 could be achieved while operating at atmospheric pressure. Selectivity (37%) and catalyst performance (TON = 69) could be further enhanced when the reaction was performed under hydrogen pressure (60 bars). A plausible mechanism based on experimental evidence is proposed.

Mo(0) complexes with aliphatic PNP-pincer ligands enable the first example of non-noble metal catalyzed formic acid disproportionation leading to methanol with a selectivity of up to 37% and a turnover number up to 69.

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

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