Enhanced CO2 Adsorption Research Articles

Development of amine-pillar[5]arene modified porous silica for CO2 adsorption, and CO2/CH4, CO2/N2 separation

Solid amine adsorbents with macrocycle are emerging as promising candidate for efficient CO2 adsorption due to their abundance of active sites, inherent cavities, and ease of encapsulation. Herein, a novel amine­pillar[5]arene functionalized porous silica adsorbent (EDA-P5S) was synthesized to investigate CO2 adsorption, the adsorption process of CO2 was executed using a fixed-bed (FD-2000) reactor. The dynamic adsorption capacities of EDA-P5S were 7.62 (0.46) and 7.72 (0.41) mmol/g for CO2/CH4 and CO2/N2, respectively, both the gas mixtures showed high separation selectivity. Subsequent research indicated that its porous structure facilitated the dispersion of amines and increased the exposure of active sites, thereby enhancing CO2 adsorption. Furthermore, the in-situ FTIR, 13C NMR spectra, and computational results collectively confirmed that the CO2 adsorption mechanism on EDA-P5S was consistent with the zwitterion mechanism. This work may provide a useful strategy for CO2 solid amine porous adsorbents to obtain high-purity CO2 by selectively removing CO2 from CH4 or N2.

Enhancement of CO2 adsorption and separation in basic ionic liquid/ZIF-8 with core-shell structure.

A novel strategy was proposed to improve the performance of gas separation in nano-materials, by fabricating a core-shell structure out of the basic ionic liquid ([Emim]2[IDA]) and zeolitic imidazolate framework (ZIF-8). The [Emim]2[IDA]/ZIF-8 exhibits a remarkable CO2 adsorption capacity of 14 cm3 g-1 at 298 K and 20 kPa, the ideal selectivity of CO2/N2 is as high as 104 and CO2/CH4 is 348 at 298 K and 100 kPa, which are much higher than the CO2 adsorption capacity (4.3 cm3 g-1) and the selectivity (SCO2/N2 = 7.4, SCO2/CH4 = 2.7) of ZIF-8. This work could pave the way for designing advanced nanostructures tailored for gas separation.

Organic-inorganic hybridization strategy for promoting BiOBr CO2 photoreduction via enhanced CO2 adsorption and photogenerated carrier migration

The low electron-hole separation efficiency and poor CO2 adsorption of BiOBr limit its photoreduction CO2 performance. In this work, BiOBr was hybridized with Ni-MOF, it shows that the Eads of BiOBr decreases from −0.36 eV to −1.73 eV, and the Gibbs free energy of CO2 adsorption decreases from 0.12 eV to −1.25 eV. In addition, the PL and TPR results reveal that the hybridization strategy accelerates the electron-hole separation rates. The CO evolution of BiOBr/Ni-MOF is 121.8 μmol g−1 h−1 when the amount of Ni-MOF is 15%, which is 5 and 7.2 times higher than BiOBr and Ni-MOF, respectively. Briefly, the CO2 adsorption and photogenerated carrier separation of inorganic materials can be improved by organic–inorganic hybridization strategy, which inspires a new direction for the design of high-performance catalysts.

Selective hydrogenation of CO2 to formic acid with higher yield in an aqueous medium with a nano-nickel-metal catalyst: reaction parameter optimization by response surface methodology (RSM)

A nano-nickel catalyst (∼21 nm) was synthesized for CO2 conversion to formic acid (FA). FA selectivity was ∼100% with a formation rate of 2245 μmol g−1 h−1. Na2CO3 acted as a promoter which enhanced CO2 adsorption and FA yield.

Catalytic conversion of carbon dioxide (CO2) using coal-based nano-carbon materials.

Carbon dioxide (CO2) is a prominent greenhouse gas and a widely available carbon resource. The chemical conversion of CO2 into high-value chemicals and fuels is a significant approach for mitigating carbon emissions and attaining carbon neutrality. However, enhancing CO2 adsorption and conversion rates remains a primary challenge in CO2 recycling. The development of high-performance catalysts is pivotal for the catalytic conversion of CO2. In this context, coal-based carbon materials, characterized by their extensive specific surface area and adaptable chemical composition, can offer more reactive active sites and have robust CO2 adsorption capabilities. They can function as either standalone catalysts or as components of composite catalysts, making them promising materials for CO2 reduction. The use of affordable and abundant coal as a precursor for carbon materials represents a crucial avenue for achieving clean and efficient coal utilization. This paper reviews the progress of research on coal-based carbon materials and examines their advantages and challenges as catalysts for CO2 reduction.

The synergy of in situ-generated Ni0 and Ni2P to enhance CO adsorption and protonation for selective CH4 production from photocatalytic CO2 reduction

The synergy between in situ-generated Ni0 sites and Ni2P selectively boosts CH4 formation by enhancing *CO adsorption and protonation.

Modification of ZnO gas-diffusion-electrodes for enhanced electrochemical CO2 reduction: optimization of operational conditions and mechanism investigation

Amino-functionalized ZnO exhibits enhanced CO2 adsorption capacity and selectivity for electrochemical conversion of CO2 to CO.

A first-principles study of electro-catalytic reduction of CO2 on transition metal-doped stanene.

Employing first-principles calculations based on density functional theory, this work examines the activity of 3d transition metal-doped stanene for electro-catalytic CO2 reduction through the first two electron transfer steps to CO. Our results related to CO2 activation, the first and a crucial step of the reduction process revealed that, among the entire 3d transition metal row studied, only Ti- and Fe-doped stanene can bind and significantly activate the CO2 molecule, while the rest of the TM single atoms are inert in activating the molecule. The activation of the CO2 molecule on Ti- and Fe-doped stanene has been observed in the presence of water as well. In addition, the formation of OCHO has been observed to be energetically preferred over COOH formation as a reaction intermediate, indicating the preference for the formate path of the reduction reaction. Furthermore, despite the strong adsorption of H2O on the catalyst surface, the presence of water seems to enhance CO2 adsorption on the catalysts, contrary to what has been observed recently in graphene-based catalysts. Finally, our difference charge density and the Bader charge calculations reveal that the ability of Ti- and Fe-doped stanene in activating the CO2 molecule and their potential catalytic activity for CO2 reduction is to be attributed to the charge transfer between the catalyst and the molecule, providing new insights into the rational design of 2D catalysts beyond graphene.

Au depositing and Mg doping synergistically regulates an In2O3 photocatalyst for promoting CO2 reduction and CH4 exclusive generation

Mg–Au bimetallic functional sites modified In2O3 nanoflowers hybrid photocatalysts with exceptional activities are successfully fabricated, attributed to the enhanced CO2 adsorption and activation ability and optimized band gap structure.

Mechanistic study of the competition between carbon dioxide reduction and hydrogen evolution reaction and selectivity tuning via loading single-atom catalysts on graphitic carbon nitride.

In the context of catalytic CO2 reduction (CO2RR), the interference of the inherent hydrogen evolution reaction (HER) and the possible selectivity towards CO have posed a significant challenge to the generation of formic acid. To address this hurdle, in this work, we have investigated the impact of different single-atom metal catalysts on tuning selectivity by employing density functional theory (DFT) calculations to scrutinize the reaction pathways. Single-atom catalysts supported on carbon-based systems have proven to be pivotal in altering both the activity and selectivity of the CO2RR. In this study, a series of single-atom-metal-loaded g-C3N4 monolayers (MCN, M = Ni, Cu, Zn, Ga, Cd, In, Sn, Pb, Ag, Au, Bi, Pd and Pt) were systematically examined. Through detailed DFT calculations, we explored their influence on reaction selectivity between the *COOH and *OCHO intermediates. Notably, NiCN favors the reaction via the *OCHO route, with a significantly lower rate-determining potential of 0.36 eV, which is approximately 73.5% lower than that of the CN system (1.36 eV). Most importantly, the Ni single-atom catalyst with lower coordination significantly enhances CO2 adsorption, promoting CO2RR over HER. Overall, this study, guided by DFT calculations, provides a theoretical prediction of how the selection of single-atom metal catalysts can effectively modulate the reaction pathway, thereby offering a potential solution for achieving high product selectivity in CO2RR.

Ionic Liquids Modulating Local Microenvironment of Ni-Fe Binary Single Atom Catalyst for Efficient Electrochemical CO2 Reduction.

The Ni and Fe dual-atom catalysts still undergo strikingly attenuation under high current density and high overpotential. To ameliorate the issue, the ionic liquids with different cations or anions are used in this work to regulate the micro-surface of nitrogen-doped carbon supported Ni and Fe dual-atom sites catalyst (NiFe-N-C) by an impregnation method. The experimental data reveals the dual function of ionic liquids, which enhances CO2 adsorption ability and modulates electronic structure, facilitating CO2 anion radical (CO2 •¯)stabilization and decreasing onset potential. The theoretical calculation results prove that the attachment of ionic liquids modulates electronic structure, reduces energy barrier of CO2 •¯ formation, and enhances overall ECR performance. Based on these merits, BMImPF6 modified NiFe-N-C (NiFe-N-C/BMImPF6) achieves the high CO faradaic efficiency of 91.9% with a CO partial current density of -120mA cm-2 at -1.0V. When the NiFe-N-C/BMImPF6 is assembled as cathode of Zn-CO2 battery, it delivers the highest power density of 2.61mW cm-2 at 2.57mA cm-2 and superior cycling stability. This work will afford a direction to modify the microenvironment of other dual-atom catalysts for high-performance CO2 electroreduction.

CO2 adsorption mechanisms at the ZIF-8 interface in a Type 3 porous liquid

Porous liquids (PLs) are an attractive material for gas separation and carbon sequestration due to their permanent internal porosity and high adsorption capacity. PLs that contain zeolitic imidazole frameworks (ZIFs), such as ZIF-8, form PLs through exclusion of aqueous solvents from the framework pore due to its hydrophobicity. The gas adsorption sites in ZIF-8 based PLs are historically unknown; gas molecules could be captured in the ZIF-8 pore or adsorb at the ZIF-8 interface. To address this question, ab initio molecular dynamics was used to predict CO2 binding sites in a PL composed of a ZIF-8 particle solvated in a water, ethylene glycol, and 2-methylimidazole solvent system. The results show that CO2 energetically prefers to reside inside the ZIF-8 pore aperture due to strong van der Waals interactions with the terminal imidazoles. However, the CO2 binding site can be blocked by larger solvent molecules that have greater adsorption interactions. CO2 molecules were unable to diffuse into the ZIF-8 pore, with CO2 adsorption occurring due to binding with the ZIF-8 surface. Therefore, future design of ZIF-based PLs for enhanced CO2 adsorption should be based on the strength of gas binding at the solvated particle surface.

Synergy tetraethylenepentamine and diethanolamine impregnated within silica nanotubes derived from natural halloysite for efficient CO2 capture

Amine-impregnated porous solid adsorbents are promising commercial CO2 capture adsorbents for CO2 mitigation due to relatively large CO2 capacity and high CO2 selectivity. However, the intrinsic viscosity and aggregation of the polyamine leads to low amine efficiency and greatly limits its further development. In this work, a facile and efficient approach was carried out to manipulate the porosity of natural halloysite (HNTs) support with hollow tubular structure and impregnate mixed-polyamines, i.e., both tetraethylenepentamine (TEPA) and diethanolamine (DEA) to synergistically enhance CO2 adsorption capacity, fast adsorption kinetics and thermal/chemical stability compared to the individual supported TEPA and DEA. The effects of the blend amount for TEPA and DEA, adsorption temperature and CO2 partial pressure on CO2 adsorption capacity and adsorption kinetics were specifically discussed. Due to the auxiliary effect of DEA, the chemical reaction between non-hydroxylated TEPA and CO2 was altered thus improving amine efficiency and the agglomeration layer between protonated TEPA molecules and carbamate, which existed due to electrostatic interaction when TEPA was loaded alone, was loosened thus improving amine efficiency and adsorption kinetics. Therefore, the maximum CO2 adsorption capacity of MHNTs loaded with 20 wt% TEPA and 20 wt% DEA was 3.25 mmol/g at 75 °C in the flow of 40 vol% N2/60 vol% CO2. Compared with loading individual TEPA with multiple amino groups on MHNTs, individual DEA with hydroxyl groups could increase the utilization efficiency of the amino groups of TEPA and ultimately obtain excellent CO2 capture capacity and adsorption kinetics. The experimental results show that the adsorbents obtained in this study using mixed amine impregnated silica nanotubes derived from natural minerals have a promising application in practical CO2 capture and separation processes.

Surface Activation by Single Ru Atoms for Enhanced High-Temperature CO2 Electrolysis.

Cathodic CO2 adsorption and activation is essential for high-temperature CO2 electrolysis in solid oxide electrolysis cells (SOECs). However, the component of oxygen ionic conductor in the cathode displays limited electrocatalytic activity. Herein, stable single Ruthenium (Ru) atoms are anchored on the surface of oxygen ionic conductor (Ce0.8 Sm0.2 O2-δ , SDC) via the strong covalent metal-support interaction, which evidently modifies the electronic structure of SDC surface for favorable oxygen vacancy formation and enhanced CO2 adsorption and activation, finally evoking the electrocatalytic activity of SDC for high-temperature CO2 electrolysis. Experimentally, SOEC with the Ru1 /SDC-La0.6 Sr0.4 Co0.2 Fe0.8 O3-δ cathode exhibits a current density as high as 2.39 A cm-2 at 1.6 V and 800 °C. This work expands the application of single atom catalyst to the high-temperature electrocatalytic reaction in SOEC and provides an efficient strategy to tailor the electronic structure and electrocatalytic activity of SOEC cathode at the atomic scale.

Surface Activation by Single Ru Atoms for Enhanced High‐Temperature CO2 Electrolysis

AbstractCathodic CO2 adsorption and activation is essential for high‐temperature CO2 electrolysis in solid oxide electrolysis cells (SOECs). However, the component of oxygen ionic conductor in the cathode displays limited electrocatalytic activity. Herein, stable single Ruthenium (Ru) atoms are anchored on the surface of oxygen ionic conductor (Ce0.8Sm0.2O2‐δ, SDC) via the strong covalent metal‐support interaction, which evidently modifies the electronic structure of SDC surface for favorable oxygen vacancy formation and enhanced CO2 adsorption and activation, finally evoking the electrocatalytic activity of SDC for high‐temperature CO2 electrolysis. Experimentally, SOEC with the Ru1/SDC‐La0.6Sr0.4Co0.2Fe0.8O3‐δ cathode exhibits a current density as high as 2.39 A cm−2 at 1.6 V and 800 °C. This work expands the application of single atom catalyst to the high‐temperature electrocatalytic reaction in SOEC and provides an efficient strategy to tailor the electronic structure and electrocatalytic activity of SOEC cathode at the atomic scale.

Porous carbon materials augmented with heteroatoms derived from hyperbranched biobased benzoxazine resins for enhanced CO2 adsorption and exceptional supercapacitor performance

Porous carbon materials doped with heteroatoms are an excellent alternative for applications in CO2 adsorption and supercapacitors. Herein, we present a new approach to obtain heteroatoms (N, O, and S) doped porous carbon materials using bio-based hyperbranched benzoxazine (RES-HP-BZ) as a precursor. Two types of porous carbon materials, poly(RES-HP-BZ)-700 and poly(RES-HP-BZ)-800, were synthesized through a simple calcination method by carbonization and KOH activation of benzoxazine at temperatures of 700 °C and 800 °C, respectively. The chemical structure, texture properties, and surface chemistry characteristics were validated through FTIR, NMR, SEM, XRD, and XPS, respectively. The resulting poly(RES-HP-BZ)-800 exhibited micro and meso porous characteristics with a high SBET of 841 m2 g−1, pore size of 1.14 nm, and pore volume of 0.70 cm3 g−1. The poly(RES-HP-BZ)-800 also showed a high graphitization degree and electrochemically energetic N-6, N-5, N-Q, O-2, and O-3 heteroatoms, which led to a high capacitance of 523 F g−1 (at 0.5 A g−1) as well as CO2 capture of 4.63 mmol g−1 at 298 K. These newly developed bio-based porous carbons derived from hyperbranched bio-benzoxazine with excellent electrochemical performance make them a promising candidate for eco-friendly supercapacitors.

Enhancing CO2 adsorption performance of porous nitrogen-doped carbon materials derived from ZIFs: Insights into pore structure and surface chemistry

In this work, a novel approach for the synthesis of porous nitrogen-doped carbon materials (PNCs) with a highly microporous structure through low-temperature carbonization of ZIF-8 and ZIF-61 assisted by KCl and NaCl is reported. The introduction of KCl and NaCl during the carbonization process can adjust the surface chemical properties and pore structures of the PNCs derived from ZIF-8 and ZIF-61. The effects of pore structures and surface groups of PNCs on CO2 adsorption capacity are explored. Results show that the cumulative pore volume in the pore size range of 5–7 Å (V5-7 Å), pyrrolic-N content, and COOH content exert favorable influences on CO2 adsorption capacity at 1 bar and 25 °C. Notably, V5-7 Å is the key factor in enhancing the CO2 adsorption capacity of PNCs. Moreover, the degree of contribution of V5-7 Å, V7-9 Å, pyrrolic-N content, pyridinic-N content, and COOH content to the CO2 adsorption capacity is evaluated by establishing a multiple linear regression equation, and the results show that on the basis of PNCs possessing optimum pore structures (V5-7 Å > 0.10 cm3/g), pyrrolic-N content in PNCs becoming the dominant contributor to CO2 adsorption capacity. The as-prepared 2CN8-KCl-600 sample demonstrates high CO2 adsorption capacity, which reaches 4.61 mmol/g at 25 °C and 6.70 mmol/g at 0 °C (1 bar), respectively. Besides, 2CN8-KCl-600 exhibits high CO2/N2 selectivity (39.5) under the typical flue gas scenario and high cycling stability. This work offers a novel perspective on preparing highly efficient carbon-based adsorbents for CO2 and provides the fundamental understanding for enhanced CO2 adsorption performance on PNCs.

Tungsten and oxygen dual vacancies regulation of the S-scheme ZnSe/ZnWO4 heterojunction with local polarization electric field for efficient CO2 photocatalytic reduction

Inefficient separation and sluggish transfer of photogenerated charges on the photocatalyst is one of the bottlenecks for CO2 photocatalytic reduction. In this study, the ZnSe/ZnWO4 heterojunction with tungsten vacancies and oxygen vacancies (ZZ-30%-Vw,o) was synthesized by hydrothermal process and post-etching method for CO2 reduction. Various characterizations showed superior structural and optical properties of the ZZ-30%-Vw,o heterojunction; results of ESR and work function calculation demonstrated that the heterojunction conformed to S-scheme charge transfer mechanism. Results of various tests and density functional theory (DFT) calculation confirmed the existence of W and O vacancies, as well as the locally polarized electric field (PEF). The PEF and the built-in electric field (IEF) could not only accelerate carriers separation and transfer, but also enhance CO2 adsorption and activation, thus enhancing photocatalytic activity toward CO2 reduction. The ZZ-30%-Vw,o composite exhibited the highest CO yield of 96.91 µmol/g/h, approximately 21.0 times of the ZnSe. Moreover, the ZZ-30%-Vw,o possessed favorable structure-performance stability. The COOH* was the most important intermediate during CO2 reduction, and possible CO2 reduction pathways and mechanism were proposed. This work paves a feasible way for improving photocatalytic activity via introducing dual surface vacancies on heterojunction photocatalysts.

Reconstruction of interface oxygen vacancy for boosting CO2 hydrogenation by Cu/CeO2 catalysts with thermal treatment

The interfacial structure of metal and oxide support plays a pivotal role in reverse water gas shift (RWGS). However, rare work investigated the factor of the metal-oxide interface during RWGS reaction. In this work, the interface of Cu/CeO2 catalysts was designed through the thermal treatment of copper nitrate salt on CeO2 with an H2 atmosphere under different temperatures, and CO2 hydrogenation performance was studied at 400 °C to investigate the effect of interfacial structure on RWGS reaction. Among these prepared catalysts, Cu/CeO2-400 catalysts achieved the best CO2 conversion activity (CO production rate 1.23 mol/gcat.h). Cu interacted with CeO2 to form Cu-O-Ce interface and induced more oxygen vacancy formation. The oxygen vacancy around the Cu-CeO2 interface enhanced CO2 adsorption and promoted CO2 conversion. CO2 reacted with active hydrogen to COOH, then COOH species dissociated into CO and OH adsorbed on the surface of Cu-CeO2. These results gave insights into the design of a highly effective catalyst for CO2 hydrogenation.

Tuning the selectivity of CO2 electroreduction on Cu/In2O3 heterogeneous interface

The electrochemical reduction of CO2 is an effective approach to reduce and utilize CO2 for carbon neutral under mild conditions, meanwhile, the development of efficient and stable catalysts with large area and low cost is more conducive to the industrialization of CO2 electroreduction. The metal-oxide heterogeneous interface can promote the activation and conversion of CO2 due to the synergy effect between the metal and the oxide. Therefore, Cu/In2O3 electrodes are fabricated by magnetron sputtering in one step to achieve high selectivity of CO or CH3OH at different potentials. The highest Faradaic efficiency of CO is 78% at − 0.75 V, and unexpectedly, the Faradaic efficiency of CH3OH at − 0.55 V can reach 56%. The abundance of heterogeneous interfaces in Cu/In2O3 provides more active sites, reduces the work function and shifts the d‐band center upward. The catalytic performance was improved by electron transfer promotion and enhanced CO adsorption. Such advantages are responsible for the unique catalytic properties of the metal-oxide electrodes and provide a novel insight to develop large area metal-oxide electrodes for CH3OH preparation.