CO Adsorption Energy Research Articles

Efficient CO2 Capture and Activation on Novel Two-Dimensional Transition Metal Borides.

The large-scale production of CO2 in the atmosphere has triggered global warming, the greenhouse effect, and ocean acidification. The CO2 conversion to valuable chemical products or its capture and storage are of fundamental importance to mitigate the greenhouse effect on the environment. Therefore, exploring new two-dimensional (2D) materials is indispensable due to their potential intriguing properties. Here, we report a new family of 2D transition metal borides (M2B2, M = Sc, Ti, V, Cr, Mn, and Fe; known as MBenes) and demonstrate their static and dynamic stability. These MBenes show a metallic nature and exhibit excellent electrical conductivity. The CO2 adsorption energy on MBenes ranges from -1.04 to -3.95 eV and exhibits the decreasing order as Sc2B2 > Ti2B2 > V2B2 > Cr2B2 > Mn2B2 > Fe2B2. The spin-polarization calculation shows a reduction in the adsorption energy for magnetic systems. Bader charge transfer indicates the formation of CO2δ- moiety on the MBene surface, so-called activated CO2, which is essential for its reaction with other surface chemicals. Differential charge density plots reveal a significant charge accumulation around the CO2 molecule. Our theoretical results predict the usage of new MBenes as a cost-effective catalyst for CO2 capture and activation.

CO2 chemisorption and dissociation on flat and stepped transition metal surfaces

As a promising and practical way to decrease CO2 emissions, the conversion of CO2 to value-added chemicals has received significant recent attention. The activation of CO2 on catalyst surfaces might proceed via a chemisorption state with a bent CO2 configuration, in which substrate electrons are transferred into the antibonding orbital of the CO2 adsorbate. Based on density functional theory calculations, we present an extensive survey of CO2 chemisorption and dissociation on flat and stepped surfaces of several transition metals. The binding energy of chemisorbed CO2 is closely correlated with the extent of electron transfer from the metal to CO2, as evidenced by a linear relationship found between the CO2 adsorption energy and its Bader charge. Transition state scaling (TSS) correlations between binding energies of transition states and binding energies of either initial or final states are found to exist for the dissociation of the chemisorbed CO2 on flat and stepped surfaces, which can be used to predict the efficacies of the catalysts. Our results show that defect sites at stepped surfaces have a strong influence on CO2 chemical activation and dissociation.

Pyrrolic N‐Stabilized Monovalent Ni Single‐Atom Electrocatalyst for Efficient CO2 Reduction: Identifying the Role of Pyrrolic–N and Synergistic Electrocatalysis

AbstractEngineering the electronic structure of metal, N‐doped carbon catalysts is a potential strategy for increasing the activity and selectivity of CO2 electroreduction reaction (CO2RR). However, establishing a definitive link between structure and performance is extremely difficult due to constrained synthesis approaches that lack the ability to precisely control the specific local environment of MNC catalysts. Herein, a soft‐template aided technique is developed for the first time to synthesize pyrrolic N4Ni sites coupled with varying N‐type defects to synergistically enhance the CO2RR performance. The optimal catalyst helps attain a CO Faradaic efficiency of 94% at a low potential of −0.6 V and CO partial current density of 59.6 mA cm−2 at −1 V. Results of controlled experimental investigations indicate that the synergy between NiN4 and metal free defect sites can effectively promote the CO2RR activity. Theoretical calculations revealed that the pyrrolic N coordinated NiN4 sites and C atoms next to pyrrolic N (pyrrolic NC) have a lower energy barrier for the formation of COOH* intermediate and optimum CO* binding energy. The pyrrolic N regulate the electronic structure of the catalyst, resulting in lower CO2 adsorption energy and higher intrinsic catalytic activity.

Interaction mechanism between CO and H2S over CuFe2O4 oxygen carrier during chemical-looping combustion: A DFT study

During the chemical-looping combustion process, CO as an important part of syngas and H2S as a common sulfur compound inevitably coexist in the fuel. Based on the density functional theory and periodic structure model, the interaction mechanism between CO and H2S over the O-defective CuFe2O4 surface was comprehensively investigated. The results show that the adsorption energies of adsorbates on the O-defective surface are in the order of S* (−205.42 kJ/mol) > HS* (−191.37 kJ/mol) > CO (−44.88 kJ/mol) > H2S* (−28.97 kJ/mol). CO adsorption over the O-defective surface is dominant as compared to H2S adsorption. The adsorption energies of CO in the presence of H2S, HS* and S* are − 73.21, −255.98 and − 105.35 kJ/mol, respectively. The adsorption strength of CO over the O-defective surface was enhanced in the presence of HS* or S*. The presence of CO* will greatly limit the H2S dehydrogenation process, especially for the second dehydrogenation step. The energy barriers of CO oxidation with the participation of H2S*, HS* and S* are 69.66, 51.42 and 14.19 kJ/mol, respectively. COS may be produced form the reaction between CO and S* with an energy barrier of 27.13 kJ/mol, following the Eley–Rideal reaction mechanism. CuFe2O4 oxygen carrier exhibits good anti-sulfur ability because the reaction of CuFe2O4 with CO and H2S kinetically prefers the CO oxidation pathway rather than the COS formation pathway.

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

Identifying Key Descriptors for the Single-Atom Catalyzed CO Oxidation

First-principle investigation of CO adsorption on Pd-loaded VO2 monolayer

Using the first principle calculation based on density functional theory, the CO adsorption on pure VO2 monolayer and Pd-loaded VO2 monolayer (Pd/VO2) investigated systematically. The electronic structure and properties of the most energetic configuration are analyzed in terms of density of states and charge density difference. The results showed that the adsorption energy of CO on pure VO2 monolayer was −0.239 eV, and the length of V–O bond did not change obviously, which indicated physisorption. Further studies showed that the adsorption energy of CO adsorption on Pd/VO2 surface was −2.010 eV, and the length of V–O bond changed significantly, indicating that CO can be chemically adsorbed on Pd/VO2 surface. Finally, the calculation of optical properties showed that the absorption of visible light by CO adsorption on VO2 monolayer can be substantially improved due to the supported Pd atom. Therefore, the supported Pd atom can effectively improve the adsorption effect of pure VO2 monolayer, providing an promising method to promote the practical application of VO2 monolayer.

Ordered mesoporous carbon spheres assisted Ru nanoclusters/RuO2 with redistribution of charge density for efficient CO2 methanation in a novel H2/CO2 fuel cell

Efficiently reducing carbon dioxide (CO2) into carbon chemicals and fuels is highly desirable due to the rapid growth of atmospheric CO2 concentration. In prior work, we described a unique H2/CO2 fuel cell driven by low-valued waste heat, which not only converts CO2 to methane (CH4) but also outputs electrical energy, yet the CO2 reduction rate needs to be urgently improved. Here, a novel Ru-RuO2 catalyst with heterostructure was grafted on mesoporous carbon spheres by in situ partially reducing RuO2 into ultrasmall Ru clusters (∼1 nm), in which heteroatom-doped carbon spheres as a matrix with excellent conductivity and abundant pores can not only easily confine the formation of Ru nanocluster but also are beneficial to the exposed active sites of Ru complex and the mass transport. Compared to pure RuO2 nanoparticles supported on carbon spheres, our composite catalyst boosts the CO2 conversion rate by more than 5-fold, reaching a value of 382.7 μmol gcat.-1h−1 at 170 ℃. Moreover, a decent output power density of 2.92 W m−2 was obtained from this H2/CO2 fuel cell using Ru-RuO2 embedded carbon spheres as a cathode catalyst. The Ru-RuO2 heterostructure can modify the adsorption energy of CO2 and induce the redistribution of charge density, thus boosting CO2 reduction significantly. This work not only offers an efficient catalyst for this novel H2/CO2 fuel cell but also presents a facile method to prepare Ru nanoclusters.

Carbon dioxide molecular interactions with hydrogenated Ni(111) surface: a DFT study

Within the density functional theory (DFT) study, we considered the contact of carbon dioxide (CO2) with the hydrogenated Ni(111) surface covered with adsorbed hydrogen. The hydrogenation of CO2 over the Ni(111) surface causes the formation of [HC(OH)2], [COOH], [HCOO], and [C(OH)2] reaction intermediates confirmed by the present DFT investigation. The formation of the [HC(OH)2] and [C(OH)2] intermediates is observed for the first time. When CO2 has approached the on-top Ni site on a partially hydrogen-covered Ni(111) surface, the [COOH] intermediate is successfully formed. Hydrogen adsorption is a reason for an increase in the CO2 adsorption energy compared to that of the CO2 adsorbed on the clean Ni(111) surface. Our results can help understand the CO2 adsorption on the nanoscale Ni metal. They will be useful in guiding experiments in developing better nanomaterials for efficient gas sensing.

CO Oxidation Catalytic Effects of Intrinsic Surface Defects in Rhombohedral LaMnO3.

There is an ongoing effort to replace rare and expensive noble-element catalysts with more abundant and less expensive transition metal oxides. With this goal in mind, the intrinsic defects of a rhombohedral perovskite-like structure of LaMnO3 and their implications on CO catalytic properties were studied. Surface thermodynamic stability as a function of pressure (P) and temperature (T) were calculated to find the most stable surface under reaction conditions (P=0.2 atm, T=323 K to 673 K). Crystallographic planes (100), (111), (110), and (211) were evaluated and it was found that (110) with MnO2 termination was the most stable under reaction conditions. Adsorption energies of O2 and CO on (110) as well as the effect of intrinsic defects such as Mn and O vacancies were also calculated. It was found that O vacancies favor the interaction of CO on the surface, whereas Mn vacancies can favor the formation of carbonate species.

Effect of Ni Doping and Vacancy Defects on the Sensing Characteristics of Graphene for NO<sub>2</sub> and CO Detection: A DFT Study

The sensing characteristics of pristine, Ni-doped, and C-vacancy graphene towards CO and NO2 gas molecules were studied using density functional theory (DFT). The adsorption energies, electronic properties, charge transfer, and stable geometries were calculated to evaluate the gas-surface interaction mechanisms. Both pristine and vacancy graphene have smaller CO and NO2 adsorption energies and charge transfer than the Ni-doped graphene, whereas the adsorption energy on Ni-doped vacancy graphene is higher than that of Ni-doped graphene. The results indicate that both CO and NO2 gas molecules only attach to pristine graphene through weak physical adsorption. Stronger chemisorption occurs when the gas molecules adsorb on the surface of vacancy, Ni-doped, and Ni-doped vacancy graphene. Additionally, the results demonstrated that Ni-doped vacancy graphene has higher sensitivity and selectivity towards the NO2.

Mechanistic Insights into the Effect of Sulfur on the Selectivity of Cobalt-Catalyzed Fischer–Tropsch Synthesis: A DFT Study

Sulfur is a common poison for cobalt-catalyzed Fischer–Tropsch Synthesis (FTS). Although its effects on catalytic activity are well documented, its effects on selectivity are controversial. Here, we investigated the effects of sulfur-covered cobalt surfaces on the selectivity of FTS using density functional theory (DFT) calculations. Our results indicated that sulfur on the surface of Co(111) resulted in a significant decrease in the adsorption energies of CO, HCO and acetylene, while the binding of H and CH species were not significantly affected. These findings indicate that sulfur increased the surface H/CO coverage ratio while inhibiting the adsorption of carbon chains. The elementary reactions of H-assisted CO dissociation, carbon and oxygen hydrogenation and CH coupling were also investigated on both clean and sulfur-covered Co(111). The results indicated that sulfur decreased the activation barriers for carbon and oxygen hydrogenation, while increasing the barriers for CO dissociation and CH coupling. Combining the results on elementary reactions with the modification of adsorption energies, we concluded that the intrinsic effect of sulfur on the selectivity of cobalt-catalyzed FTS is to increase the selectivity to methane and saturated short-chain hydrocarbons, while decreasing the selectivity to olefins and long-chain hydrocarbons.

Insights into Interaction of CO\(_2\) with N and B-doped Graphenes

Graphene is a promising candidate for CO2 capture and storage. Doping graphene with other elements is an effective way to modify its CO2 storage ability. The literature has shown that the N and B doping could change the adsorption strength of CO2 on the graphene substrate. However, there is no research available to elucidate the adsorption sites and the physical properties underlying the interaction of CO2 with the N and B doped systems. Therefore, this paper is devoted to clarifying the current topic using the self-consistent van der Waals density functional theory calculations. The results showed that the N and B doping increases and decreases the adsorption energy of CO2, respectively. The reason is that there are more peaks of the electronic density of states of CO2 participating in the interaction with the N p orbital than with the B p orbital.

A new nitrogen-enriched biochar modified by ZIF-8 grafting and annealing for enhancing CO2 adsorption

To increase the CO2 adsorption capacity of biochar, a facile modification method of biochar is proposed. Through in-situ synthesis and annealing (< 500 °C), ZIF-8 (zeolitic imidazolate frameworks) was successfully grafted onto biochar to form nitrogen-enriched modified biochar. The results show that the in-situ synthesis method improves the dispersion of ZIF-8 nanoparticles and the modified biochar inherits the parental characteristics of high nitrogen content of ZIF-8 (>10 at.%). Compared with raw biochar, the pore structure of modified biochar was significantly improved: the maximum surface area was increased from 10 to 882 m2/g. The biochar modified by ZIF-8 grafting and annealing of 400 °C (MNBC3–400) shows the highest CO2 dynamic adsorption capacity of 1.8 mmol/g at 30 °C and 1 bar and it is regenerable and stable during 10 cycles of CO2 adsorption-desorption. Moreover, MNBC3–400 also exhibits the maximum CO2 uptake of nearly 2 mmol/g from CO2 adsorption isotherms and the highest CO2/N2 selectivity of 16.0 at 25 °C and 1 bar. The density functional theory (DFT) results show that the modified biochar has a higher CO2 adsorption energy than the parent materials and the van der Waals effect is dominant in the CO2 adsorption system.

Interfacial engineering of worm-shaped palladium nanocrystals anchored on polyelectrolyte-modified MXene nanosheets for highly efficient methanol oxidation

The development of high-efficiency methanol oxidation electrocatalysts with acceptable costs is central to the practical use of direct methanol fuel cell. In this work, a convenient interfacial engineering strategy is developed to the design and construction of quasi-one-dimensional worm-shaped palladium nanocrystals strongly coupled with positively-charged polyelectrolyte-modified Ti3C2Tx MXene (Pd NWs/PDDA-MX) via the direct electrostatic attractions. Because of the intriguing structural features including ultrathin-sheet nature, homogeneous Pd dispersion, numerous grain boundaries, strong electronic interaction, and high metallic conductivity, the as-fabricated Pd NWs/PDDA-MX hybrid shows superior electrocatalytic performance with a large electrochemically active surface area of 105.3 m2 g−1, a high mass activity of 1526.5 mA mg−1, and reliable long-term durability towards alkaline methanol oxidation reaction, far outperforming the commercial Pd nanoparticle/carbon catalysts. Density functional theory calculation further demonstrate that there are strong electronic interactions in the Pd nanoworm/Ti3C2Tx model with a depressed CO adsorption energy, thereby guaranteeing a stable interfacial contact as well as strong antitoxic ability.

CO2 adsorption enhancement over alkaline metal-promoted MgO with SO2, O2, and H2O present: A theoretical study

Protective effect of alkaline metals on CO 2 adsorption disturbed by SO 2 /O 2 /H 2 O. • SO 2 /O 2 /H 2 O adsorption on alkaline metal-promoted MgO is more intense than pure MgO. • SO 2 /O 2 /H 2 O aggregate around alkaline metals and save other adsorption sites for CO 2 . • Alkaline metals change surface potential fields of MgO in favor of CO 2 adsorption. • Involvement of alkaline metals helps to optimize electron transmission paths of CO 2 . • Desorption temperatures of CO 2 over promoted MgO increase due to strong adsorption. The oxidizing abilities of SO 2 /O 2 and molecular polarity of H 2 O severely hamper CO 2 adsorption on MgO via capturing surface electrons or occupying active sites. Therefore, it is crucial for MgO to gain better anti-SO 2 /O 2 /H 2 O features. In this study, alkaline metals are introduced as promoters for MgO to counter negative effects of SO 2 /O 2 /H 2 O. Through density functional theory (DFT) calculations, adsorption structures/energies, electron clouds/electron transfer, effects of temperatures are fully investigated to account for how adverse impacts of SO 2 /O 2 /H 2 O are counteracted. Based on DFT calculation results, the average adsorption energies of CO 2 on pure MgO are only 0.46, −6.54, and 2.41 kJ/mol with SO 2 , O 2 , and H 2 O present, respectively. For Li-promoted MgO, the average adsorption energy of CO 2 rises by about 65.51 kJ/mol with H 2 O present. As to Na-doped MgO, its average CO 2 adsorption energy is raised by around 200 % with SO 2 involved. As far as K-modified MgO is concerned, the average adsorption energy of CO 2 is almost 5.0 times as big as the counterpart with O 2 . Regarding Rb-amended MgO, its average adsorption strength of CO 2 is raised to about −38.55 kJ/mol when being affected by H 2 O/SO 2 /O 2 . What is more, it is proved that the desorption temperatures of CO 2 rise a lot over promoted MgO owing to stronger electronic interaction. The research results could provide meaningful information for applying promoted MgO as a CO 2 capturer in real industries.

Interfacial chemical bond modulated Bi19S27Br3/g-C3N4 Z-scheme heterojunction for enhanced photocatalytic CO2 conversion

Direct Z-scheme heterojunction can primely facilitate separation efficiency of the photogenerated carriers and maximize the redox ability of as-prepared photocatalyst, which has been regarded as one of the promising strategies to increase photocatalytic CO2 conversion efficiency. Herein, a novel interfacial C-S bond modulated Z-scheme heterojunction Bi19S27Br3/g-C3N4 composite is constructed to accelerate the photogenerated electron transfer from g-C3N4 to Bi19S27Br3, offering much more excited reductive electrons to the surface of Bi19S27Br3 where owns lower CO2 adsorption energy, which is more conducive to CO2 reduction conversion. Without adding sacrificial agent or photosensitizer, the photocatalytic CO2 conversion to CO yield of Bi19S27Br3/g-C3N4 reaches up to 12.87 μmol g−1 h−1, which is 5 and 4-fold of Bi19S27Br3 and g-C3N4, respectively. This study provides the new insight in precisely tailoring photogenerated charge separation direction by establishing chemical bond in direct Z-scheme structure for CO2 photoreduction.

Nitrogen vacancies enriched Ce-doped Ni3N hierarchical nanosheets triggering highly-efficient urea oxidation reaction in urea-assisted energy-saving electrolysis

Urea oxidation reaction (UOR), which has favorable thermodynamic energy barriers compared with oxygen evolution reaction (OER), can provide more cost-effective electrons for the renewable energy systems, but is trapped by its sluggish UOR kinetics and intricate reaction intermediates formation/desorption process. Herein, we report a novel and effective electrocatalyst consisting of carbon cloth supported nitrogen vacancies-enriched Ce-doped Ni3N hierarchical nanosheets (Ce-Ni3N@CC) to optimize the flat-footed UOR kinetics, especially the stiff rate-determine CO2 desorption step of UOR. Upon the introduction of valance state variable Ce, the resultant nitrogen vacancies enriched Ce-Ni3N@CC exhibits an enhanced UOR performance where the operation voltage requires only 1.31 V to deliver the current density of 10 mA cm−2, which is superior to that of Ni3N@CC catalyst (1.36 V) and other counterparts. Density functional theory (DFT) results demonstrate that the incorporation of Ce in Ni3N lowers the formation energy of nitrogen vacancies, resulting in rich nitrogen vacancies in Ce-Ni3N@CC. Moreover, the nitrogen vacancies together with Ce doping optimize the local charge distribution around Ni sites, and balance the adsorption energy of CO2 in the rate-determining step (RDS), as well as affect the initial adsorption structure of urea, leading to the superior UOR catalytic performance of Ce-Ni3N@CC. When integrating the Ce-Ni3N catalyst in UOR//HER and UOR//CO2R flow electrolyzer, both of them perform well with low operation voltage and robust long-term stability, proofing that the thermodynamically favorable UOR can act as a suitable substitute anodic reaction compared with that of OER. Our findings here not only provide a novel UOR catalyst but also offer a promising design strategy for the future development of energy-related devices.

Boron‐Rich Boron Nitride Nanotubes as Highly Selective Adsorbents for Selected Diatomic Air Pollutants: A DFT Study

AbstractBoron‐rich boron nitride nanotubes (BN‐BNNTs), which have boron antisite defects (BN), adsorb gas molecules more favorably as compared to their pristine counterparts because of the localized states of antisites. Using computational chemistry methods, the structural, adsorptive, and electronic properties of selected diatomic air pollutants (CO, NO, and SO) on BN‐BNNT (8,0), with a particular focus on the antisites, are investigated. It is found that CO adsorbs on BN with 180° angle (∠BNCO) while NO and SO adsorb with 142° angle (∠BNNO) and 116° angle (∠BNSO), respectively. This difference is ascribed to the repulsive interaction originated from lone pair electrons on N and S. Adsorption energy of CO, NO, and SO molecules dominates over that of O2 and N2 and is independent of their radii of BN‐BNNTs. The practical capacity of these pollutant molecules is calculated to be ≈5 mmol g–1 (14 wt%) under ambient conditions. Therefore, our results show that BN‐BNNT can be used as a highly selective adsorbent for diatomic air pollutants. BN‐BNNT as sensing materials in terms of change in bandgap and work function through the adsorption is also discussed.

Carbon dioxide storage and separation using all-boron B38 fullerene: DFT calculations

The adsorption behaviorof CO2 molecules on B38 fullerene isinvestigated using density functional theory calculations. It is found that CO2 molecules act as a Lewis acid and are chemisorbed on the B-B bond surrounding the hexagon holes of B38. The stability of the CO2 adsorbed structures is assessed at different temperatures and pressures. Under P0 = 0.1 Mpa, the CO2 adsorption capacity of B38 is 17.04 and 2.43 mol/kg(B38) at T = 200 and 300 K, respectively. The larger adsorption energy of CO2 compared to H2, N2, and CH4 molecules suggests that B38 fullerene might be used to separate CO2 from gas mixtures.

Machine learning-based prediction of the adsorption energy of CO on boron-doped graphene

To accurately and quickly investigate the adsorption ability of different boron-doped graphene for CO, 1864 different sets of CO adsorption energy on boron-doped graphene were obtained by simulation, and an overall framework based on machine learning was proposed.