Adsorption Of Molecular O2 Research Articles

Catalytic oxidation of lignite by Pt/TiO2 can enhance cadmium adsorption capacity

Addressing global warming necessitates innovative strategies in fossil fuel management. This study evaluates lignite, a low-rank coal with limited calorific value, exploring applications beyond its use as fuel. Utilizing Pt/TiO2 catalytic oxidation, the research aims to enhance the cadmium adsorption capacity of lignite in wastewater. Lignite, treated with 0.5% Pt/TiO2 at 125 °C for 2 h, demonstrated a threefold increase in cadmium adsorption capacity. Characterization using TGA-DSC confirmed the modification process as exothermic and self-sustainable. Spectroscopic analysis and Boehm titration revealed significant alterations in pore structure, surface area, and oxygen-containing functional groups, emphasizing the effectiveness of catalytic oxidation. Adsorption mechanisms such as complexation, cation exchange, and cation-π interactions were identified, enhancing Cd adsorption. Techniques, including the d-band model, H2-TPR, and O2-TPD, indicated that dissociative adsorption of molecular O2 and the subsequent generation of reactive oxygen species introduced additional oxygen-containing functional groups on the lignite surface. These findings provide essential strategies for the alternative use of lignite in environmental remediation, promoting sustainable resource utilization and enhancing cost-effectiveness in remediation processes. Environmental implicationThis study innovates in using lignite to reduce cadmium (Cd) contamination in wastewater. Employing Pt/TiO2 catalytic oxidation, lignite is transformed, enhancing its cadmium adsorption capacity. This process, being exothermic, contributes to decreased energy consumption. The approach not only mitigates the hazardous impacts of cadmium but also aligns with sustainability by reducing greenhouse gas emissions and energy use, showcasing a multifaceted environmental advancement.

Understanding the adsorption behavior of oxygen on the 3C–SiC(1 1 0) surface: A first‐principles study

The adsorption behavior of atomic oxygen and molecular O2 on the 3C–SiC(1 1 0) surface is investigated by first-principles calculations. The atomic O prefers to be adsorbed at the C top site (C–O) with adsorption energy of −1.95 eV after zero-point energy correction, followed by the C–O–Si bridge site, Si–O–Si bridge site, and the Si top site (Si–O) with adsorption energies of −1.46, −1.36, and −1.13 eV, respectively. The molecular O2 separately trapped by the second nearest neighboring C and Si atoms (C–O–O–Si, M4 type) is the most stable configuration with the adsorption energy of −2.46 eV, which is followed by the Si–O–O–Si (M5 type), C–O–O–Si (M3 type), O–Si–O (M2 type), and Si–O=O (M1 type) configurations with the adsorption energies of −2.24, −1.87, −1.07, and −0.75 eV, respectively. All these molecular O2 adsorption configurations exhibit high tendency to dissociate with the dissociation barriers range of 0.09–0.19 eV. The adsorbed atomic O seems to be easily trapped at the C–O site due to the extremely low diffusion barrier. In addition, the infrared spectra of all the atomic O and molecular O2 adsorption configurations are predicted and compared with available experimental observations.

Decorating Single-Atomic Mn Sites with FeMn Clusters to Boost Oxygen Reduction Reaction.

The regulation of electron distribution of single-atomic metal sites by atomic clusters is an effective strategy to boost their intrinsic activity of oxygen reduction reaction (ORR). Herein we report the construction of single-atomic Mn sites decorated with atomic clusters by an innovative combination of post-adsorption and secondary pyrolysis. The X-ray absorption spectroscopy confirms the formation of Mn sites via Mn-N4 coordination bonding to FeMn atomic clusters (FeMnac /Mn-N4 C), which has been demonstrated theoretically to be conducive to the adsorption of molecular O2 and the break of O-O bond during the ORR process. Benefiting from the structural features above, the FeMnac /Mn-N4 C catalyst exhibits excellent ORR activity with half-wave potential of 0.79 V in 0.5 M H2 SO4 and 0.90 V in 0.1 M KOH as well as preeminent Zn-air battery performance. Such synthetic strategy may open up a route to construct highly active catalysts with tunable atomic structures for diverse applications.

Decorating Single‐Atomic Mn Sites with FeMn Clusters to Boost Oxygen Reduction Reaction

AbstractThe regulation of electron distribution of single‐atomic metal sites by atomic clusters is an effective strategy to boost their intrinsic activity of oxygen reduction reaction (ORR). Herein we report the construction of single‐atomic Mn sites decorated with atomic clusters by an innovative combination of post‐adsorption and secondary pyrolysis. The X‐ray absorption spectroscopy confirms the formation of Mn sites via Mn‐N4coordination bonding to FeMn atomic clusters (FeMnac/Mn‐N4C), which has been demonstrated theoretically to be conducive to the adsorption of molecular O2and the break of O−O bond during the ORR process. Benefiting from the structural features above, the FeMnac/Mn‐N4C catalyst exhibits excellent ORR activity with half‐wave potential of 0.79 V in 0.5 M H2SO4and 0.90 V in 0.1 M KOH as well as preeminent Zn‐air battery performance. Such synthetic strategy may open up a route to construct highly active catalysts with tunable atomic structures for diverse applications.

Catalytic modification of corn straw facilitates the remediation of Cd contaminated water and soil

Turning postharvest residue into high-value-added products is crucial for agricultural waste management and environmental remediation. In this proof-of-concept study, nanosized Pt/TiO2 was used as a model catalyst to modify corn straw (CS) materials through a simple low-temperature oxidation process. This method was demonstrated to be self-sustainable, waste-free, and with high yields. At an optimal temperature of 220 °C, O2 treatment with 1 wt% Pt/TiO2 greatly changed ultra-micropore and mesopore structures, dissolved organic carbon, aromatic contents and surface oxygen (O)-containing functional groups in CS products. This treatment resulted in an approximately 5-fold increase of cadmium (Cd) adsorption from aqueous solution and immobilization rate of 43.1% at 7d for bioavailable Cd in soil. Spectroscopic and linear regression analysis demonstrated that both acidic and basic functional groups in CS contributed to Cd adsorption, suggesting chemical adsorption. According to the d-band theory, the unexpected role of catalysts in CS modification could be associated with dissociative adsorption of molecular O2 on the Pt surface. These results provide insights for the development of economic and sustainable technologies to reutilize agricultural waste biomass for water and soil remediation.

Role of bimetallic Au-Ir subnanometer clusters mediating O2 adsorption and dissociation on anatase TiO2 (101).

A comprehensive computational study on the oxygen molecule (O2) adsorption and activation on bimetallic Au-Ir subnanometer clusters supported on TiO2(101)- up to five atoms in size-is performed. A global optimization density functional theory-based basin-hopping algorithm is used to determine putative global minima configurations of both mono- and bimetallic clusters supported on the metal oxide surface for all sizes and compositions. Our results indicate a strong cluster-oxide interaction for monometallic Ir clusters with calculated adsorption energy (Eads) values ranging from -3.11 to -5.91eV. Similar values are calculated for bimetallic Au-Ir clusters (-3.21 up to -5.69eV). However, weaker Eads values are calculated for Au clusters (ranging from -0.66 to -2.07eV). As a general trend, we demonstrate that for supported Au-Ir clusters on TiO2(101), those Ir atoms preferentially occupy cluster-oxide interface positions while acting as anchor sites for the Au atoms. The overall geometric arrangements of the putative global minima configurations define O2 adsorption and dissociation, particularly involving the monometallic Au5 and Ir5 as well as the bimetallic Au2Ir3 and Au3Ir2 supported clusters. Spontaneous O2 dissociation is observed on both Ir5 and on the Ir-metallic part of Au3Ir2 and Au2Ir3 supported clusters. This is in sharp contrast with supported Au5, where a large activation energy is needed (1.90eV). Interestingly, for Au5, we observe that molecular O2 adsorption is favorable at the cluster/oxide interface, followed by a smaller dissociation barrier (0.71eV). From a single cluster catalysis point of view, our results have strong implications in the ongoing understanding of oxide supported bimetallic while providing a useful first insight into the continuous in silico design of novel subnanometer catalysts.

Resolving the adsorption of molecular O2 on the rutile TiO2(110) surface by noncontact atomic force microscopy

Interaction of molecular oxygen with semiconducting oxide surfaces plays a key role in many technologies. The topic is difficult to approach both by experiment and in theory, mainly due to multiple stable charge states, adsorption configurations, and reaction channels of adsorbed oxygen species. Here we use a combination of noncontact atomic force microscopy (AFM) and density functional theory (DFT) to resolve [Formula: see text] adsorption on the rutile [Formula: see text](110) surface, which presents a longstanding challenge in the surface chemistry of metal oxides. We show that chemically inert AFM tips terminated by an oxygen adatom provide excellent resolution of both the adsorbed species and the oxygen sublattice of the substrate. Adsorbed [Formula: see text] molecules can accept either one or two electron polarons from the surface, forming superoxo or peroxo species. The peroxo state is energetically preferred under any conditions relevant for applications. The possibility of nonintrusive imaging allows us to explain behavior related to electron/hole injection from the tip, interaction with UV light, and the effect of thermal annealing.

Oxygen vacancies confined in conjugated polyimide for promoted visible-light photocatalytic oxidative coupling of amines

Conjugated polyimide (R-PI) containing triazine ring was synthesized by a modified thermal solid-state polymerization of the salt monomer. The structure of the as-prepared R-PI was characterized by FTIR, XPS, EPR, EA and solid-state 13C NMR, which is rich in oxygen vacancies (OVs). The R-PI exhibits excellent catalytic performance for selective benzylamine oxidation reactions under visible light. Both experimental and theoretical calculation results indicated that the introduction of OVs could increase the level of electron delocalization of R-PI. R-PI possess more excitable electrons and a narrower band gap, which expands the absorption of long-wavelength light. The surface OVs also serve as excellent sites for molecular O2 adsorption and activation. Chemisorbed O2 spatially builds up a channel for the delivery of photoexcited electrons to O2, which effectively enhanced separation efficiency of photogenerated charge carriers. These results indicate that OVs-rich conjugated polyimides can be efficient visible light-responsive photocatalysts for green synthesis.

Atom-Coordinated Structure Triggers Selective H2O2 Production

The family of atomic catalysts in defective carbons is now of increasing interest for diverse reactions. In this issue of Chem, Liu and co-workers unveil the nature of M–N–C (M = Mn, Fe, Co, Ni, and Cu) as active sites that can finely tune the oxygen reduction reaction (ORR) pathways spanning 1e–4e transfer processes.

Cornstalk-Derived Nitrogen-Doped Partly Graphitized Carbon as Efficient Metal-Free Catalyst for Oxygen Reduction Reaction in Microbial Fuel Cells

The low electrocatalytic activity for oxygen reduction reaction (ORR) and the high cost of cathode catalyst in microbial fuel cells (MFCs) are the important factors that limit the practical applications. The metal-free nitrogen (N)-doped partly graphitized carbon (NPGC) as cathode catalyst is prepared at different temperatures (700-1050 °C) by using waste cornstalks as the carbon source and melamine as the N source. Scanning electron microscopy, X-ray diffraction, specific surface areas, and transmission electron microscopy have been used, in parallel with electrochemical activity tests including rotating disk electrode (RDE) and power output, to clarify how the active constituents and structure of NPGC influence the MFCs performance. Carbonization temperature has a significant effect on the porous structure and N-doped defects (pyridinic, pyrrolic, and graphitic N), which correspondingly influence the amount of active sites, ORR activity and long-time running durability in MFCs. The abundant functional oxygen-containing groups in the porous structure (1177.76 m2 g-1) of NPGC (1000 °C) contribute to the fast adsorption of molecular O2 onto the carbon skeleton. The N-induced charge delocalization facilitates the chemisorption of O2 and cleavage of O-O bonds to effectively enhance the four-electron O2 reduction on NPGC electrode. The maximum power density of NPGC-1000 is 1122 mW m-2 in MFCs, which is higher than that of Pt/C (988 mW m-2), and only has a decline of 10.2% after 80 days. This work provides a metal-free, high-efficiency, and cost-effective ORR electrocatalyst for MFCs.

A comparative DFT study on the CO oxidation reaction over Al- and Ge-embedded graphene as efficient metal-free catalysts

In the present study, by means of density functional theory (DFT) calculations, the catalytic oxidation of CO by O2 molecule is investigated over Al- and Ge-embedded graphene. The large atomic radius of these dopant atoms can induce a local surface curvature and modulate the electronic structure properties of the graphene sheet through the charge redistribution. It is found that the adsorption of molecular O2 over Al- or Ge-embedded graphene is stronger than that of CO molecule. The CO oxidation reaction by molecular O2 on Al- and Ge-embedded graphene is comparably studied. The results indicate that a two-step process can occur, namely, CO+O2→CO2+Oads and CO+Oads→CO2. Furthermore, the computed activation energy (Eact) for the first reaction on Ge-doped graphene is lower than that of Al-doped one, and the formation of second CO2 molecule on both surfaces can occur rapidly due to its low energy barrier (0.1eV).

Surface chemistry of oxygen on aluminum--Performance of the density functionals: PBE, PBE0, M06, and M06-L.

We investigated the performance of the density functional theory (DFT) functionals PBE, PBE0, M06, and M06-L for describing the molecular and dissociative adsorption of O2 onto pure and doped Al(111) surfaces. Adsorption of O2 was studied at the perfect Al(111) surface and compared with the case where an additional Al atom was present as an adatom. Additionally, we studied how these functionals perform when different dopants are present at the Al(111) surface in two distinct geometries: as an adatom or as a substitutional atom replacing an Al atom. The performance of the different functionals is greatly affected by the surface geometry. The inclusion of Hartree-Fock exchange in the functional leads to slight differences in adsorption energies for molecular adsorption of O2 . These differences become very pronounced for dissociative adsorption, with the hybrids PBE0 and M06 predicting more exergonic adsorption than PBE and M06-L. Furthermore, PBE0 and M06 predicted trends in adsorption energies for defective and perfect surfaces which are in line with the experimental knowledge of the effects of surface defects in adsorption energies. The predictions of the non-hybrids PBE and M06-L point in the opposite direction. The analysis of the contributions of the van der Waals (vdW) forces to the adsorption energies reveals that the PBE and PBE0 functionals have similar difficulties in describing vdW interactions for molecular adsorption of O2 while the M06 functional can give a description of these forces with an accuracy which is at least similar to that of the correction of the D3 type.

Trends in the Reactivity of Molecular O2 with Copper Clusters: Influence of Size and Shape

The adsorption and dissociation of molecular O2 on copper clusters of varying size and morphology (Cun with n = 3–8, 13, and 38 atoms) has been systematically investigated using several DFT approaches. Different modes of adsorption of molecular O2 are found for each atomicity of the copper clusters, with their relative stability depending on the cluster morphology: bridge conformations are stabilized on planar clusters, while hollow h-100 and h-111 modes are preferentially formed on 3D clusters. O2 adsorption energies correlate with the HOMO energy of the isolated copper clusters but not with their atomicity. On the other hand, the degree of activation of the O–O bond, and therefore the activation energy barrier necessary to break it, depends on the charge transferred to the π* MO of O2, which in turn is determined by the mode of adsorption of O2 on the metal. Cluster morphology appears then as the key factor determining the catalytic activity of copper, since the most activating h-111 and h-100 adsorptio...

Molten LiCl Layer Supported on MgO: Its Possible Role in Enhancing the Oxidative Dehydrogenation of Ethane

Molten lithium chloride, supported on various oxides, promotes the catalytic activity for oxidative dehydrogenation (ODH) of ethane. As a first step toward understanding these systems, we use ab initio molecular dynamics to examine the solvation of ethane, ethylene, oxygen, and water in molten lithium chloride supported on magnesium oxide. Among these molecules, only water dissolves readily in molten LiCl. Possible reactions between O2 and LiCl(l) have been studied in an effort to identify an intermediate for the ODH mechanism. We found that the formation of LiClO, LiO2, Li2O, LiOH, and Cl2 requires a substantial increase in the free energy; therefore, we propose that they are not reaction intermediates for ODH. The only process that cannot be ruled out is molecular adsorption of O2 at the LiCl/MgO interface.

A density functional study on interaction of first-row transition-metal dicarbides, C2X (X = Sc-Zn) with O2

We present our calculations based on density functional theory to explore the molecular adsorption of O2 on the first-row transition-metal dicarbides C2X (X=Sc-Zn). Degree of activation of O2 is observed to be less in C2XO2 (X=Sc-V) as compared with C2XO2 (X=Cr-Zn) except for X=Cu, and is marked by the amount of total charge on O2. Topological analysis shows that the interaction in the cases of C2XO2 (X=Sc-V) is prominent between X and O and mostly being intermediate type whereas in C2XO2 (X=Cr-Zn), both CO and XO bondings are observed with shared-kind and intermediate characteristics respectively.

Density functional theory calculations on oxygen adsorption on the Cu2O surfaces

In order to understand various surface properties such as corrosion and potential catalytic activity of Cu2O surfaces in the presence of environmental gases, we report here spin-polarized density functional theory calculations of the adsorptions of atomic and molecular oxygen on three surface Cu2O facets. Atomic oxygen adsorbs at the hollow site formed with copper atoms of Cu2O(111), while its adsorption on the Cu2O(110) and Cu2O(100) induces surface reconstruction. Molecular oxygen adsorbs on one coordinated unsaturated surface copper atom and two coordinated saturated copper atoms of Cu2O(111), on the top of two surface copper atoms of Cu2O(110), and on four surface copper atoms on Cu2O(100). It was found that atomic O and molecular O2 adsorption on the Cu2O(100) surface is stronger than on the Cu2O(111) surface. Atomic O and molecular O2 adsorption on the surface of Cu2O(111) induces magnetism. This is different from other systems previously known to exhibit point defect ferromagnetism. On all three surfaces, dissociative adsorption was found to be energetically favorable.

Oxygen Adsorption on Au–Ni(111) Surface Alloys

Molecular O2 dissociates upon interaction with a Ni(111) surface, as the spatial and energetic overlap between the Ni 3d electrons and the O2 antibonding orbitals is quite favorable. On a Au–Ni(111) surface alloy where the extent of this overlap is greatly reduced, exposure to O2 results in adsorption of molecular O2 characterized by three peroxo- or superoxo-like vibrational bands centered at 743, 856, and 957 cm–1 as observed by high resolution electron energy loss spectroscopy. These bands correspond to the stretch vibrational mode of O2 at respective adsorption sites of type pseudo-3-fold fcc/hcp, degenerate-pseudo-2-fold fcc/hcp and bridge, and pseudo-3-fold bridge. These unusual chemical environments are brought about by surface alloying, rather than the presence of Au clusters on Ni, and are further stabilized by a dramatic reconstruction of the top two surface layers, as explained with an idealized surface alloy model in conjunction with electronic structure considerations. The ability to adjust t...

Interaction of third-row main group dicarbides, C2X (X = K–Br) with molecular oxygen: A density functional study

In this work, we present our calculations, based on density functional theory (DFT) to investigate the molecular adsorption of O2 on the third-row main group dicarbides, C2X, with X=K, Ca, Ga, Ge, As, Se, Br. The structures of the host C2X clusters, except C2Ga and C2Ge, are found to be weakly modified in presence of O2 adsorbate. C2Ga and C2Ge clusters which show cyclic ground-state structures become linear while interacting with O2 molecule. It is observed that the O–O stretching frequencies in C2XO2 are red-shifted in comparison to that in O2 molecule, whereas the C–C stretching frequencies are found to be increased. The calculated adsorption (Eads) and Gibbs’ free energies (dG) for the clusters with even number of electrons are found to follow the order of C2CaO2>C2GeO2>C2SeO2, whereas the increase in O–O bond lengths follows the reverse order, i.e. (O–O)C2SeO2>(O–O)C2GeO2>(O–O)C2CaO2. On the other hand, for the clusters with odd number of electrons, Eads and O–O bond lengths follows almost the same order. Existence of disynaptic basins V (C,O) and their corresponding lower relative fluctuation and higher covariance values based on ELF topological analysis infers that the electrons are delocalized in these areas giving rise to shared-electron interactions. In addition, large electron density at the bond critical point (BCP) between C (of host cluster) and O (of adsorbate) also infers the C–O bonding to be shared-type. This fact is also found to be supported by large delocalization index for C and O as compared to that for X and O.

A computational DFT study of CO oxidation on a Au nanorod supported on CeO2(110): on the role of the support termination

Possible reaction paths for CO oxidation on ceria-supported Au nanoparticle catalysts were modeled by placing a Au nanorod on a CeO2(110) surface. The results are discussed against experimental and computational data in the literature for Au/CeO2 with emphasis on the role of the ceria surface termination and involvement of ceria lattice oxygen atoms. Three CO oxidation mechanisms were modeled using density functional theory calculations: (i) reaction of adsorbed CO with ceria lattice O atoms (Mars–van Krevelen mechanism), (2) reaction of adsorbed CO with co-adsorbed O2 (co-adsorption mechanism) and (3) dissociation of adsorbed O2 followed by CO oxidation (stepwise mechanism). All three candidate mechanisms are relevant to CO oxidation catalysis as they exhibit nearly similar overall reaction barriers. The Mars–van Krevelen mechanism is consistent with experimental findings on the involvement of lattice O atoms in CO oxidation. This mechanism is prohibitive for CeO2(111) because of too high oxygen vacancy formation energy. Besides, the specific surface termination of CeO2(111) prevents O2 adsorption at its interface with Au due to repulsive interactions with the lattice O atoms. Molecular O2 adsorption is possible on CeO2(110) because of the presence of Ce4+ ions in the top layer of the surface. O2 adsorption can occur on a defective Au/CeO2(111) surface (J. Am. Chem. Soc., 2012, 134, 1560), because exposed Ce3+ ions are available. However, it is established here that O2 dissociation will heal the vacancies and deactivate Au supported on the CeO2(111) surface. The importance of Mars–van Krevelen and stepwise mechanisms in CO oxidation by Au/CeO2 strongly depends on the surface plane of the ceria support.

Interaction of second-row dicarbides with molecular oxygen: A theoretical study

In this work, we report our calculations, based on density functional theory (DFT) to investigate the molecular adsorption of O2 on the second-row dicarbides, C2X, with X=Na, Mg, Al, Si, S, P, and Cl. It is found that all the second-row dicarbides, except C2Si, almost retain their structures while reacting with O2 molecule, whereas the ground-state structure of C2Si which is reported to be cyclic, however, becomes linear in presence of O2. Similarly, the ground-state structure of C2S cluster which is reported to be triplet becomes singlet while interacting with O2 molecule, with the triplet state 1.08eV higher in energy. The O–O stretching frequencies in the complex C2XO2 are red-shifted as compared to that in O2 molecule, whereas the C–C stretching frequencies are observed to increase. Negative adsorption and Gibb’s free energies indicate that the adsorptions are thermodynamically favorable. Moreover, the existence of disynpatic basins V (C,O) and their corresponding higher covariance values based on ELF topological analysis infers that the electrons are delocalized in these areas giving rise to shared-electron interactions.