CO2 Adsorption Research Articles

Enhanced electrocatalytic CO2 reduction into formate: Unleashing the effect of engineered bimetallic oxides supported on activated carbon

The excessive concentration of anthropogenic CO2 continuously harms the atmosphere. Consequently, deploying CO2 via the electrochemical reduction approach has become a highly sought-after research thrust area. In this study, a facile, one-pot solution combustion synthesis method (SCSM) was employed for the synthesis of various mixed-metal oxides supported on porous activated carbon (SnO2-CuO@AC). The prepared materials are characterized by analytical and spectroscopic techniques. Electrochemical studies were performed for the SnO2-CuO@AC catalyst to reduce CO2 into formic acid via an electrochemical approach. The in-depth properties of the designed catalysts were analysed by theoretical calculations using FT-IR and XRD data. The SnO2-CuO@AC exhibited improved electrochemical performance with a high current density of −10.77 mAcm−2, a low overpotential of −1.29 V, a lower Tafel slope value of 100 mV/dec. The faradaic efficiency for formic acid was 78.8 % at 1.3 V vs. RHE, with high stability for 9 h. The presence of coordinated active sites and oxygen vacancies, and a lower Tafel slope, also endorses CO2 adsorption and activation, faster electron transfer and boosts CO2 reduction. The significant reactivity toward CO2 reduction is attributed to the intensity of interaction between CO2∗- and the electrocatalyst, followed by kinetic activation toward protonation to obtain the desired product.

Modified Biochar Materials From Eucalyptus globulus Wood as Efficient CO2 Adsorbents and Recyclable Catalysts

AbstractHighly porous carbon materials derived from renewable resources constitute a promising and sustainable strategy regarding the enhancement of CO2 capture technologies. In this work, the valorization of Eucalyptus globulus wood, a forest invasive species present in European forests, is performed through its transformation in biochar. The deposition of nitrogen and different metals (aluminum, copper and chromium) onto biochar is performed, using the magnetron sputtering as a pioneering technique, to produce coated biochar nanoparticles with improved properties. The resultant modified biochar particles maintain a highly porous structure and present a remarkable CO2 adsorption capacity (up to 4.80 mmol g−1 for N@BC), which is attributed to the synergy of their large total surface area (527 m2 g−1) and microporosity (pore diameter = 21 Å), with a high content of nitrogen and oxygen heteroatom moieties (40.4% N, 11.4% O). Their application as heterogeneous bifunctional catalysts in CO2 cycloaddition to epichlorohydrin is performed, in the absence of any solvent or co‐catalyst, under moderate conditions (20 bar CO2, 120 °C), leading to good conversions (up to 58% conversion) and excellent selectivity for cyclic carbonates. Cu‐coated biochar is shown to be more stable than non‐modified material, being recycled and reused along 4 consecutive runs without loss of catalytic activity or selectivity.

Highly active ternary Ir/In2O3-ZrO2 catalyst for CO2 hydrogenation towards methanol: The role of zirconia

Indium oxide supported iridium catalyst has been verified to be highly active and selective for CO2 hydrogenation to methanol. In this work, zirconia is introduced into the Ir/In2O3 system as a novel Ir/In2O3-ZrO2 ternary catalyst. The solid solution generated between ZrO2 and In2O3 exhibits a strong electronic metal-support interaction with iridium, rendering the supported iridium species highly dispersed in a form of clusters. Thereout, an active interface between iridium and the solid-solution carrier is thus generated, on which electron transport is more feasible with a stronger CO2 adsorption than that of on the Ir−In2O3 interfacial site. Moreover, compared to Ir/In2O3, this ternary catalyst exhibits better catalytic activity as well as the stability. Density functional theory (DFT) simulations, combined with the in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies, further demonstrate the CO-hydrogenation pathway is the most favored for methanol synthesis, providing a rationale for the superior methanol selectivity of the Ir/In2O3-ZrO2 catalyst during CO2 hydrogenation.

Tailoring tea residue-derived nitrogen-doped activated carbon for CO2 adsorption: influence of activation temperature and activating agents.

Embracing CO2 mitigation strategies, such as state-of-the-art CO2 capture technologies, is essential for effectively reducing atmospheric carbon levels and advancing global efforts toward a more sustainable future. In this context, adsorption sequestering techniques utilising carbon materials have emerged as promising candidates for CO2 capture. These materials have been extensively researched with a range of tuning methods to optimise their physicochemical features. In this study, an alteration of the N-doped activated carbon was successfully performed, utilizing tea residue as the carbon precursor and ammonia as the nitrogen source, facilitated through an impregnation procedure. With the objective of discovering the effect of diverse activation parameters on prepared adsorbent physicochemical properties, several selections of activating agents (AA) were investigated: KOH, H3PO4, ZnCl2, and NaOH, together with broad thermal activation temperature from 873 to 1173K. The best-performed adsorbents from the respective AC group were subjected to several characterisation analyses and found to the enhanced structural features, heteroatom doped-rich surface (i.e. N and O); together with AA-induced metal/mineral functionalization, the NaOH-used AC (NAC-N-1173) was the optimum-performed adsorbent with a promising 4.12mmol/g CO2 uptake capacity, higher than other prepared adsorbent including N-doped tea residue-derived char and commercialized AC with 175 and 325% higher, respectively.

Boron-Doping Engineering in AgCd Bimetallic Catalyst Enabling Efficient CO2 Electroreduction to CO and Aqueous Zn-CO2 Batteries.

The limited adsorption and activation of CO2 on catalyst and the high energy barrier for intermediate formation hinder the development of electrochemical CO2 reduction reactions (CO2RR). Herein, this work reports a boron (B) doping engineering in AgCd bimetals to alleviate the above limitations for efficient CO2 electroreduction to CO and aqueous Zn-CO2 batteries. Specifically, the B-doped AgCd bimetallic catalyst (AgCd-B) is prepared via a simple reduction reaction at room temperature. A combination of in situ experiments and density functional theory (DFT) calculations demonstrates that B-doping simultaneously enhances the adsorption and activation of CO2 and reduces the binding energy of the intermediates by moderating the electronic structure of bimetals. As a result, the AgCd-B catalyst exhibits a high CO Faraday efficiency (FECO) of 99% at -0.8V versus reversible hydrogen electrode (RHE). Additionally, it maintains a FECO over 92% at a wide potential window of 600mV (-0.6 to -1.1V versus RHE). Furthermore, the AgCd-B catalyst coupled with the Zn anode to assemble aqueous Zn-CO2 batteries shows a power density of 20.18mW cm-2 and a recharge time of 33h.

Molecular Simulation of Cyclohexane in Nanoporous Materials: Adsorption of Conformers and Coadsorption with Water and Carbon Dioxide.

Molecular simulation is used to investigate the adsorption of an organic molecule and its different conformers into various nanoporous adsorbents. In more detail, we perform grand canonical Monte Carlo simulations to determine the adsorption isotherms for cyclohexane with its three conformers (chair, boat, and twisted boat) at three different temperatures into a molecular model of active carbons and two metal-organic frameworks (MOFs) (Cu-BTC and Al-Fum). By considering the adsorption of each conformer separately, we show that the adsorption isotherms are weakly dependent on the molecular conformation. When considering the concomitant adsorption of the three conformers under realistic conditions (to verify the population of each conformer in bulk mixtures), we show that the chair conformer is predominantly adsorbed in each material. However, such favorable adsorption mostly reflects the fact that this conformer has the largest population in the bulk mixture under the same thermodynamic conditions. On the contrary, with an increase in the cyclohexane gas pressure, the adsorption of boat and twisted boat conformers increases, while that of the chair conformer decreases as packing (entropy) effects become predominant during confinement. The adsorption of cyclohexane in the active carbon and MOF materials is also considered in the presence of water and CO2 atmospheres. In the case of the Al-fumarate material, the material is found to be strongly organophilic so that water and CO2 adsorption are negligible, and cyclohexane adsorption is not affected by competitive adsorption under any considered thermodynamic condition. On the contrary, for the active carbon and Cu-BTC material, competitive adsorption between cyclohexane and water or CO2 is observed even if cyclohexane adsorption remains preferred. While the different molecules coexist in the adsorbed phase at low pressures, increasing the cyclohexane pressure beyond 103 Pa promotes cyclohexane adsorption concomitantly with water and/or CO2 desorption.

A Synopsis on CO2 Capture by Synthetic Hydrogen Bonding Receptors.

Carbon dioxide (CO2) is one of the most abundant greenhouse gases in Earth's atmosphere and responsible for global warming. Therefore, aerial CO2 capture and sequestration has become a major task for human community. Though several adsorbents for CO2 including activated carbon, zeolites, metal-organic frameworks (MOFs), and other surface-modified porous materials are well developed, the supramolecular approaches using synthetic hydrogen-bonding receptors are less explored. This review article highlights the synthetic development of various artificial receptors and their properties toward fixation of aerial CO2 as carbonate (CO3 2-), bicarbonate (HCO3 -), or carbamate (-NHCOO-/>NCOO-) ions, induced by excess fluoride (F-) or hydroxide (OH-) ions as their tetrabutylammonium salts. The utilization of encapsulated carbonate/bicarbonate/carbamate complexes in anion exchange metathesis for separation of oxyanions from aqueous solutions are also discussed. In addition, the release of CO2 and regeneration of receptor molecules are described in a number of occasions. Most importantly, the formation of anion complexes as crystalline materials in solid-state is described in terms of supramolecular chemistry and correlated with their solution-state properties. Finally, the types of receptors containing various functional groups are scrutinized in CO2 uptake, storage, and release processes and hints of endeavours for future research are delineated.

Biogenic Synthesis of Cr‐Doped NiO/Clay Composite for Improved Dye Removal and CO2 Capture Studies

AbstractThe current work was designed to eliminate reactive yellow 18 dye (RY‐18) via adsorption from water, and CO2 from the gas stream, using the tragacanth gum‐based Cr doped NiO N.P.s/Clay (GCNC) composite. The one‐pot synthesis approach was used to produce the adsorbent, and physical and chemical properties were assessed using techniques like XRD, FTIR, UV‐visible spectroscopy, SEM, DLS, Zeta Potential, and adsorption–desorption isotherm. The GCNC composite demonstrated an impressive adsorption potential and percentage removal of 398 mg/g and 91.28%, respectively. Temkin and intraparticle diffusion models with R2 values of 0.98401 and 0.99918 were the most effective at fitting the experimental adsorption model. The thermodynamics parameters, including the change in enthalpy (H), entropy (S), and Gibbs free energy (G), demonstrated the endothermic and spontaneous nature of the adsorption process. A positive H value indicates an endothermic process, while a negative G value indicates a spontaneous process. According to the isotherms fitting model, the capacity for adsorbing CO2 at 25 °C and 1 atm was 4.8 mmol/g. The significant correlation between the slope in the log‐linear plot of the isosteric heat of adsorption and CO2 adsorption performance indicates that the isosteric heat of adsorption can be used as a predictive tool for CO2 adsorption performance. These significant results underscore the potential of the GCNC composite to revolutionize the water treatment field and CO2 capture, offering hope for a more sustainable and cleaner future.

Solid‐phase synthesis of silicalite‐1 molecular sieve based on fly ash and its CO2 adsorption performance

AbstractIn this work, an alkali melting‐pickling assisted solid phase synthesis method of S‐1 zeolite molecular sieve with excellent adsorption properties for CO2 was successfully developed by using solid waste fly ash. SiO2 with a purity of up to 97.84% was successfully extracted by using alkaline fusion activation, high temperature calcination and pickling. The CO2 adsorption capacity of the prepared SiO2 was 0.51 mmol/g at 298 K and 1 bar. Silicalite‐1 molecular sieve was prepared by solid phase synthesis method using SiO2 extracted from fly ash as silicon source. The results showed that the prepared Silicalite‐1 had good morphology and relatively high crystallinity. The specific surface area is 623.30 m2/g, and the total pore volume is 0.31 cm3/g. In addition, the adsorption capacity of CO2 was 2.05 mmol/g at 298 K and 1 bar. Compared with the prepared SiO2, the adsorption capacity of CO2 by Silicalite‐1 molecular sieve increased by four times. Moreover, under the test condition of 298 K, it has a high selectivity coefficient for CO2/N2 mixed gas, and after 10 times of adsorption‐desorption cycle tests, the adsorption capacity of Silicalite‐1 molecular sieve for CO2 does not change significantly, and its adsorption rate can still be as high as 89.31%. The results indicate that Silicalite‐1 molecular sieve prepared by solid phase synthesis method has good adsorption selectivity and adsorption–desorption cycle regeneration stability, and can be used in the field of CO2 adsorption, separation and purification. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

N-doped Porous Carbon Derived from the Pyrolysis of a Polydopamine-coated Hypercross-linked Polymer for Enhanced CO2 Adsorption.

Porous carbon materials can simultaneously capture and convert carbon dioxide, helping to reduce greenhouse gas emissions and using carbon dioxide as a feedstock for the production of valuable chemicals or fuel. In this work, a series of N-doped porous carbons (PDA@HCP(x:y)-T) was prepared; the CO2 adsorption capacity of the prepared PDA@HCP(x:y)-T was enhanced by coating polydopamine (PDA) on a hypercross-linked polymer (HCP) and then adjusting the mass ratio of PDA to HCP and the carbonization temperature. The results showed that the prepared PDA@HCP(1:1)-850 exhibited a high CO2 adsorption capacity due to abundant micropores (0.6762 cm3/g), a high specific surface area (1220.8 m²/g), and moderate surface nitrogen content (2.75%). Notably, PDA@HCP(1:1)-850 exhibited the highest CO2 uptake of 6.46 mmol/g at 0 °C and 101 kPa. Critically, these N-doped porous carbons can also be used as catalysts for the reaction of CO2 with epichlorohydrin to form chloropropylene carbonate, with chloropropylene carbonate yielding up to 64% and selectivity of the reaction reaching 94%. As a result, these N-doped porous carbons could serve as potential candidates for CO2 capture and conversion due to their high reactivity, excellent CO2 uptake, and good catalytic performance.

Influence of the chemical activation with KOH/KNO3 on the CO2 adsorption capacity of activated carbons from pyrolysis of cellulose

Plant biomass is an attractive precursor to prepare activated carbons with high surface area for CO2 adsorption due to its low-cost and easy regeneration. Despite this interest, there are still remaining questions regarding the optimal processing conditions and the choice of activating agent. Moreover, since plant biomass shows a highly variable proportion of different biopolymers (cellulose, hemicellulose, lignin), it is important to understand the activation effect on each constituent. In this work, carbons obtained from pyrolysis of cellulose were activated using two potassium salts, using two different activation temperatures. The samples were characterized to elucidate the influence of the activation conditions on their CO2 adsorption capacity. In general, all the carbons activated at higher temperature showed higher adsorption capacity. These results are comparable with other carbons derived from biomass described in the bibliography. Among the activated carbons studied, the carbon activated only with KOH exhibits the highest CO2 adsorption capacity at 1 bar meanwhile the highest adsorption capacity at saturation pressure belongs to the carbon activated with larger ratio of KNO3.

Dual Metallosalen-based Covalent Organic Frameworks for Artificial Photosynthetic Diluted CO2 Reduction.

Directly converting CO2 in flue gas using artificial photosynthetic technology represents a promising green approach for CO2 resource utilization. However, it remains a great challenge to achieve efficient reduction of CO2 from flue gas due to the decreased activity of photocatalysts in diluted CO2 atmosphere. Herein, we designed and synthesized a series of dual metallosalen-based covalent organic frameworks (MM-Salen-COFs, M: Zn, Ni, Cu) for artificial photosynthetic diluted CO2 reduction and confirmed their advantage in comparison to that of single metal M-Salen-COFs. As a results, the ZnZn-Salen-COF with dual Zn sites exhibits a prominent visible-light-driven CO2-to-CO conversion rate of 150.9 μmol g-1 h-1 under pure CO2 atmosphere, which is ~6 times higher than that of single metal Zn-Salen-COF. Notably, the dual metal ZnZn-Salen-COF still displays efficient CO2 conversion activity of 102.1 μmol g-1 h-1 under diluted CO2 atmosphere from simulated flue gas conditions (15% CO2), which is a record high activity among COFs- and MOFs-based photocatalysts under the same reaction conditions. Further investigations and theoretical calculations suggest that the synergistic effect between the neighboring dual metal sites in the ZnZn-Salen-COF facilitates low concentration CO2 adsorption and activation, thereby lowering the energy barrier of the rate-determining step.

Flame-Resistant Inorganic Films by Self-Assembly of Clay Nanotubes and their Conversion to Geopolymer for CO2 Capture.

Self-assembling of very long natural clay nanotubes represents a powerful strategy to fabricate thermo-stable inorganic thin films suitable for environmental applications. In this work, self-standing films with variable thicknesses (from 60 to 300µm) are prepared by the entanglement of 20-30µm length Patch halloysite clay nanotubes (PT_Hal), which interconnect into fibrosus structures. The thickness of the films is crucial to confer specific properties like transparency, mechanical resistance, and water uptake. Despite its completely inorganic composition, the thickest nanoclay film possesses elasticity comparable with polymeric materials as evidenced by its Young's modulus (ca. 1710MPa). All PT_Hal-based films are fire resistant and stable under high temperature conditions preventing flame propagation. After their direct flame exposure, produced films do not show neither deterioration effects nor macroscopic alterations. PT_Hal films are employed as precursors for the development of functional materials by alkaline activation and thermal treatment, which generate highly porous geopolymers or ceramics with a compact morphology. Due to its high porosity, geopolymer can be promising for CO2 capture. As compared to the corresponding inorganic film, the CO2 adsorption efficiency is doubled for the halloysite geopolymeric materials highlighting their potential use as a sorbent.

Self-Inhibition Phenomena in Cu3Pt Oxidation by CO2.

This study investigates the oxidation behavior of Cu3Pt(100) in CO2 using a combination of ambient-pressure X-ray photoelectron spectroscopy, mass spectroscopy, and density functional theory modeling. Our in situ measurements reveal the simultaneous oxidation and reduction of Cu2O due to the opposing effects of atomic oxygen and CO generated from dissociative CO2 adsorption, leading to a dynamic equilibrium state of simultaneously occurring redox reactions. Complementary atomistic calculations elucidate the inhibitory effects of subsurface Pt enrichment and the counteracting roles of CO2 and CO in surface oxidation and reduction. These results provide mechanistic insights into the dissociative pathway of CO2 molecules and dynamic evolution of surface composition and reactivity of Cu-based alloy catalysts in CO2-rich environments, with broader implications for tuning gas-surface reactions by manipulating gas reactants or solid surface composition.

Dual Metallosalen‐based Covalent Organic Frameworks for Artificial Photosynthetic Diluted CO2 Reduction

Directly converting CO2 in flue gas using artificial photosynthetic technology represents a promising green approach for CO2 resource utilization. However, it remains a great challenge to achieve efficient reduction of CO2 from flue gas due to the decreased activity of photocatalysts in diluted CO2 atmosphere. Herein, we designed and synthesized a series of dual metallosalen‐based covalent organic frameworks (MM‐Salen‐COFs, M: Zn, Ni, Cu) for artificial photosynthetic diluted CO2 reduction and confirmed their advantage in comparison to that of single metal M‐Salen‐COFs. As a results, the ZnZn‐Salen‐COF with dual Zn sites exhibits a prominent visible‐light‐driven CO2‐to‐CO conversion rate of 150.9 μmol g−1 h−1 under pure CO2 atmosphere, which is ~6 times higher than that of single metal Zn‐Salen‐COF. Notably, the dual metal ZnZn‐Salen‐COF still displays efficient CO2 conversion activity of 102.1 μmol g−1 h−1 under diluted CO2 atmosphere from simulated flue gas conditions (15% CO2), which is a record high activity among COFs‐ and MOFs‐based photocatalysts under the same reaction conditions. Further investigations and theoretical calculations suggest that the synergistic effect between the neighboring dual metal sites in the ZnZn‐Salen‐COF facilitates low concentration CO2 adsorption and activation, thereby lowering the energy barrier of the rate‐determining step.

Important structural parameter for curvature effect of TM-N4 embeded C70 fullerenes as electrocatalysts for CO2 reduction interpreted with machine learning and first-principles calculations

In this work, TM-N4 sites embedded on curved C70 Fullerenes (TMN4(n)@C64, n = 1–5 which denote the doping positions and TM = Sc-Zn) were designed as efficient catalysts for electrochemical CO2 reduction reaction (ECO2RR). With interpretable machine learning (ML) and first-principles calculations, the performance of TM-N4 sites as possible electrocatalysts for ECO2RR under the curvature effect were revealed. After the screen procedure of catalyst stability, CO2 activation and selectivity of 50 designed systems, VN4(3), CrN4(3), MnN4(2), FeN4(2, 3, 5)@C64 were identified as high performance catalysts for ECO2RR to CH4, with limiting potential of -0.41 V, -0.26 V, -0.28 V, -0.35 V, -0.25 V and -0.17 V respectively, outperform the TM-N4 catalysts on the flat surface. A key structural descriptor K which can reflect the curvature effect of TM-N4 sites on the curved surface was identified with ML models. The gradient boosting regression (GBR) and sure independence screening and sparsifying operator (SISSO) algorithm reveal that the structural parameter K have strong association with the CO2 adsorption and significant influence on the selectivity of catalysts. Interestingly, the structural parameter K can influence more the binding of O-bonded intermediates than C-bonded intermediates. With the GBR algorithm, an effective model for the prediction of the limiting potential for C1 products were obtained. This study clarified the curvature effect of TM-N4 supported on the curved surface, and provides valuable guidance for the designing of TM-N4 single atom catalysts for ECO2RR on curved surface.

Comparison of micron- and nano-sized zeolite NaY composited with bamboo charcoal and their application in CO2 adsorption

This is the first report on synthesizing nano-sized zeolite NaY dispersed on acid-refluxed bamboo wood. The nano-sized NaY on the composite was produced by increasing the alkalinity in the seed gel. The as-synthesized composite was carbonized to convert the wood to charcoal and tested in CO2 adsorption. The CO2 adsorption capacity of nano- and micron-sized NaY composites was 2.30 and 1.25 mmol/g-composite. Moreover, nano-sized NaY composite shows higher adsorption capacity per gram of zeolite than bared nano-sized NaY. The dispersion of nano-sized zeolite on carbonaceous substrates could be an efficient strategy for enhancing CO2 adsorption.

Enhanced photocatalytic CO2 reduction to CH4 on oxygen vacancy-rich NiCo2O4 with surface pits: Synthesis, DFT calculations, and mechanistic insights

Unraveling the influence of surface microstructure in materials on their interaction with CO2 remains a critical challenge in achieving efficient and selective CO2 reduction. In this study, we report the engineering of pit structures on the NiCo2O4 surface for efficient photocatalytic reduction of CO2. Characterization results show that calcination temperature affects the distribution of surface pits and oxygen vacancy concentration. Oxygen vacancy sites accompanying surface pits facilitate the generation and movement of photogenerated electrons and holes, preventing their recombination and promoting the conversion of CO2. The CH4 yield from photocatalytic CO2 reduction reaches 52.4 μmol g−1 with the optimal pitted NiCo2O4 catalyst (PNCO2), significantly surpassing the 18.4 μmol g−1 yield of non-pitted NiCo2O4 (NPNCO). Additionally, PNCO2 improves selectivity from 81.8 % for NPNCO to 94.1 %. Density functional theory calculations show that CO2 adsorption on the PNCO2 surface is significantly enhanced as the d-band center shifts toward the Fermi level. The adsorbed CO2 combines with electrons enriched at the Ni sites at the edges of the surface pits, leading to further activation. The reduction of CO2 to intermediate products such as CHO* is analyzed based on in situ diffuse reflectance infrared Fourier transform spectroscopy, and a possible reaction pathway is proposed. This work offers fresh insights into engineering surface pit structures for the design and synthesis of catalysts for photocatalytic CO2 reduction.

CO2 hydrogenation over Fe-Mn-Zn spinel oxide nanohybrids precatalysts

Catalytic CO2 hydrogenation using green hydrogen is a promising approach for mitigating CO2 emissions and utilizing CO2 as a feedstock. While Fe-based catalysts produce long-chain hydrocarbons under high-pressure CO2 hydrogenation reactions, the C2+ hydrocarbon yield tends to be insufficient at low-pressure conditions over the catalyst. This study reports the enhancement of light olefin selectivity of CO2 hydrogenation over Fe-based catalysts at low pressure via nanoscale hybridization with manganese (Mn) and zinc (Zn) oxides. The resulting hybridized catalyst exhibited distinctive performance in terms of CO2 hydrogenation to light olefins at relatively low pressure (0.7 MPa) in terms of CO2 conversion rate and C2–C4 yield with high olefin rates. Mn and Zn incorporation in Fe oxide decreased the reduction temperature, forming more Fe carbide phase. CO2 adsorption capability at relevant temperatures seems to be improved when Mn and Zn are present. This mixed oxide precatalyst approach can be extended to other elements.

DFT based investigations on inherent CO2 adsorption and direct dissociation capability of Ti2C and Nb2C mxenes

Transition metal carbide MXenes, specifically Ti2C and Nb2C, have been investigated for their ability to efficiently adsorb and dissociate CO2 using First Principles Calculations based on Density Functional Theory (FPS-DFT). Pure Ti2C and Nb2C sheets were studied with the adsorption of 1 to 4 CO2 molecules, and the results were analyzed for each case. For 4 CO2 molecules adsorbed on Ti2C and Nb2C sheets, the weight percentage (wt%) ratio was found to be 21.39% and 14.33%, respectively. The Density of States (DOS) analysis revealed that, upon CO2 adsorption, the CO2 molecule dissociates into CO and O atoms on the MXene surface. The CO molecule showed no significant hybridization with the host sheet atoms, whereas the O atom exhibited strong hybridization with the MXene surface. Transition State (TS) profiles illustrated the dissociation steps on both Ti2C and Nb2C surfaces. Phonon calculations confirmed the dynamic stability of both pure and CO2 adsorbed MXenes. Molecular Dynamics (MD) simulations conducted at 900 K indicated uniform temperature and Mean Square displacement (MSD) profiles, suggesting the stability of both pure and CO2 adsorbed MXenes at elevated temperatures, as well as uniform CO2 adsorption behavior. The adsorption energies for Ti2C and Nb2C sheets were calculated to be in the range of -1.89 to -2.77eV, suggesting that the adsorption process is favorable, spontaneous, and predominantly involves chemisorption. These findings indicate that Ti2C and Nb2C MXenes, in their intrinsic forms, are promising candidates for CO2 adsorption and dissociation technologies.