Interaction Of Molecular Oxygen Research Articles

Catalytic activity of MoO3:V2O5 mixed oxides towards oxidation reactions: the nature of catalytic centers

Singlet oxygen emission and peroxide generation at the surface of molybdenum–vanadium oxides evidenced that the catalytic activity of a MoO3:V2O5 mixed oxide at 70–175 °C was governed by the formation of peroxo groups in the interaction of molecular oxygen with adjacent Viv surface centers; the thermolysis of these groups yielded singlet oxygen capable of oxidizing selectively alcohols to aldehydes.

Особенности взаимодействия молекулярного кислорода с поверхностью конденсации в плазме дугового разряда низкого давления

A model has been developed for studying the features of the thermal interaction of molecular oxygen in the near-surface condensation layer in the plasma of a low-pressure arc discharge. It was found that the input power and pressure of the gas mixture exert the main influence on the electron temperature and on the density of positive ions (O_2^+ and O+). It is shown that at a fixed pressure, the ion density increases with an increase in the power of the system, and vice versa.

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.

Density functional theory study of the structural and bonding mechanism of molecular oxygen (O2) with C3Si

The investigations of pure and heteroatom doped carbon clusters have created great interest because of their enormous prospective applications in various research zones, for example, optoelectronics, semiconductors, material science, energy storage devices, astro-science and so on. In this article, the interaction of molecular oxygen (O2) with C3Si has explored within a density functional theory (DFT). Different possible types of structure for C3SiO2 have collected. Among five different kinds of structure, the structure-1a, A11 is more energetically stable. The nature of the bonding of O2 and C3Si, in C3SiO2 has been studied by using Bader's topological analysis of the electron charge density distribution ρ(r), Laplacian ∇2ρ(r) and total energy density H(r) at the bond critical points (BCPs) of the structures within the framework of the atoms in molecules theory (AIM). The bonding mechanism of O2 and C3Si in C3SiO2 prompts to the fundamental understanding of the interaction of C3Si with oxygen molecule. It is interesting to note that, two types of bonding mechanism are established in same C3SiO2 system such as (i) shared-kind interactions (ii) closed-shell interactions. From various kinds of structure, CC bonds in all structures are shown as shared-kind interactions whereas CSi, OO bonds are classified as closed-shell type interactions with a certain degree of covalent character.

Interaction of Molecular Oxygen with a Hexagonally Reconstructed Au(001) Surface

Kinetics of molecular oxygen/Au(001) surface interaction has been studied at high temperature and near atmospheric pressures of O2 gas with in situ X-ray scattering measurements. We find that the hexagonal reconstruction (hex) of Au(001) surface lifts to (1 × 1) in the presence of O2 gas, indicating that the (1 × 1) is more favored when some oxygen atoms present on the surface. The measured lifting rate constant vs temperature is found to be highest at intermediate temperature exhibiting a “volcano”-type behavior. At low temperature, the hex-to-(1 × 1) activation barrier (Eact = 1.3(3) eV) limits the lifting. At high temperature, oxygen adsorption energy (Eads = 1.6(2) eV) limits the lifting. The (1 × 1)-to-hex activation barrier (Ehex = 0.41(14) eV) is also obtained from hex recovery kinetics. The pressure–temperature (PT) surface phase diagram obtained in this study shows three regions: hex at low P and T, (1 × 1) at high P and T, and coexistence of the hex and (1 × 1) at the intermediate P and T.

The interaction of molecular oxygen on LaO terminated surfaces of La2NiO4

The surface composition and electronic structure of perovskite related oxides play a significant role in their electro-catalytic behaviour.

Ab initio molecular dynamics simulations of the O2/Pt(1 1 1) interaction

The interaction of molecular oxygen with Pt(111) has been studied using ab initio molecular dynamics simulations based on periodic density functional theory (DFT) calculations. The adsorption probability has been determined as a function of the initial kinetic energy and the surface temperature. In addition, the effect of coupling the substrate to a thermostat has been studied. In agreement with experiment, no direct dissociation event has been observed in the molecular dynamics simulations. Characteristic discrepancies between theory and experiment are identified which are related to the choice of the functional used in the DFT calculations. At low kinetic energy and low surface temperature trapping into a weakly bound molecular state was observed that has not been identified before.

Involvement of molecular oxygen in the donor-side photoinhibition of Mn-depleted photosystem II membranes.

It has been shownby Khorobrykh et al. (Biochemistry (Moscow)67:683-688, 2002); Yanykin et al. (Biochim Biophys Acta 1797:516-523, 2010); Khorobrykh et al. (Biochemistry 50:10658-10665, 2011) that Mn-depleted photosystem II (PSII) membrane fragments are characterized by an enhanced oxygen photoconsumption on the donor side of PSII which is accompanied with hydroperoxide formation and it was suggested that the events are related to the oxidative photoinhibition of PSII. Experimental confirmation of this suggestion is presented in this work. The degree of photoinhibition was determined by the loss of the capability of exogenous electron donors (Mn(2+) or sodium ascorbate) to the reactivation of electron transport [measured by the light-induced changes of chlorophyll fluorescence yield (∆F)] in Mn-depleted PSII membranes. The transition from anaerobic conditions to aerobic ones significantly activated photoinhibition of Mn-depleted PSII membranes both in the absence and in the presence of exogenous electron acceptor, ferricyanide. The photoinhibition of Mn-depleted PSII membranes was suppressed upon the addition of exogenous electron donors (Mn(2+), diphenylcarbazide, and ferrocyanide). The addition of superoxide dismutase did not affect the photoinhibition of Mn-depleted PSII membranes. It is concluded that the interaction of molecular oxygen (rather than superoxide anion radical formed on the acceptor side of PSII) with the oxidized components of the donor side of PSII reflects the involvement of O2 in the donor-side photoinhibition of Mn-depleted PSII membranes.

Взаємодія молекулярного кисню з поверхнею Si(001), вкритою моношарами хрому та титану

Взаємодія молекулярного кисню з поверхнею Si(001), вкритою моношарами хрому та титану

Exploring the radical nature of a carbon surface by electron paramagnetic resonance and a calibrated gas flow.

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date back to the early 1980s the focus of these early papers primarily characterized the changes to the structures under extremely harsh conditions (pH or temperature)(1-3). It is also known that paramagnetic molecular oxygen undergoes a Heisenberg spin exchange interaction with stable radicals that extremely broadens the EPR signal(4-6). Recently, we reported interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP(7). As flows of He, CO2, and N2 had a similar effect these interactions occur at the surface area of the macropore system. This manuscript highlights the experimental techniques, work-up, and analysis towards affecting the existing stable radical nature in the carbon structures. It is hoped that it will help towards further development and understanding of these interactions in the community at large.

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date back to the early 1980s the focus of these early papers primarily characterized the changes to the structures under extremely harsh conditions (pH or temperature)1-3. It is also known that paramagnetic molecular oxygen undergoes a Heisenberg spin exchange interaction with stable radicals that extremely broadens the EPR signal4-6. Recently, we reported interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP7. As flows of He, CO2, and N2 had a similar effect these interactions occur at the surface area of the macropore system. This manuscript highlights the experimental techniques, work-up, and analysis towards affecting the existing stable radical nature in the carbon structures. It is hoped that it will help towards further development and understanding of these interactions in the community at large.

Adsorption and reactions of O2 on anatase TiO2.

CONSPECTUS: The interaction of molecular oxygen with titanium dioxide (TiO2) surfaces plays a key role in many technologically important processes such as catalytic oxidation reactions, chemical sensing, and photocatalysis. While O2 interacts weakly with fully oxidized TiO2, excess electrons are often present in TiO2 samples. These excess electrons originate from intrinsic reducing defects (oxygen vacancies and titanium interstitials), doping, or photoexcitation and form polaronic Ti(3+) states in the band gap near the bottom of the conduction band. Oxygen adsorption involves the transfer of one or more of these excess electrons to an O2 molecule at the TiO2 surface. This results in an adsorbed superoxo (O2(-)) or peroxo (O2(2-)) species or in molecular dissociation and formation of two oxygen adatoms (2 × O(2-)). Oxygen adsorption is also the first step toward oxygen incorporation, a fundamental reaction that strongly affects the chemical properties and charge-carrier densities; for instance, it can transform the material from an n-type semiconductor to a poor electronic conductor. In this Account, we present an overview of recent theoretical work on O2 adsorption and reactions on the reduced anatase (101) surface. Anatase is the TiO2 polymorph that is generally considered most active in photocatalysis. Experiments on anatase powders have shown that the properties of photoexcited electrons are similar to those of excess electrons from reducing defects, and therefore, oxygen on reduced anatase is also a model system for studying the role of O2 in photocatalysis. Experimentally, the characteristic Ti(3+) defect states disappear after adsorption of molecular oxygen, which indicates that the excess electrons are indeed trapped by O2. Moreover, superoxide surface species associated with two different cation surface sites, possibly a regular cation site and a cation close to an anion vacancy, were identified by electron paramagnetic resonance spectroscopy. On the theoretical side, however, density functional theory studies have consistently found that it is energetically more favorable for O2 to adsorb in the peroxo form rather than the superoxo form. As a result, obtaining a detailed understanding of the nature of the observed superoxide species has proven difficult for many years. On reduced anatase (101), both oxygen vacancies and Ti interstitials have been shown to reside exclusively in the susbsurface. We discuss how reaction of O2 with a subsurface O vacancy heals the vacancy while leading to the formation of a surface bridging dimer defect. Similarly, the interaction of O2 with a Ti interstitial causes migration of this defect to the surface and the formation of a surface TiO2 cluster. Finally, we analyze the peroxo and superoxo states of the adsorbed molecule. On the basis of periodic hybrid functional calculations of interfacial electron transfer between reduced anatase and O2, we show that the peroxide form, while energetically more stable, is kinetically less favorable than the superoxide form. The existence of a kinetic barrier between the superoxo and peroxo states is essential for explaining a variety of experimental observations.

Molecular Mechanism of Oxygen Isotopic Exchange over Supported Vanadium Oxide Catalyst VOx/TiO2

Detailed molecular mechanisms of oxygen isotopic exchange over VOx/TiO2 catalyst following the R0, R1, and R2 mechanisms were studied using periodic DFT analysis of possible pathways by the CI-NEB method. The electronic structures of surface VOx species formed on the VOx/TiO2 model surface after interaction of molecular oxygen with fully oxidized O═V5+–O–V5+═O sites and reduced V3+–O–V3+ sites were analyzed. We found a number of metastable surface structures that are potential intermediates in the exchange reaction pathways. We present evidence that adsorption of two gas-phase oxygen molecules on a reduced V3+–O-V3+ site leads to the formation of a superoxide complex, followed by its transformation into a peroxide complex with low activation energy about E* = 0.04 eV (0.92 kcal/mol). Subsequent transformation of this surface superoxide-peroxide species follows the Langmuir–Hinshelwood mechanism without participation of lattice oxygen along the R0 reaction pathway. We demonstrate that adsorption of molecul...

Oxygen reduction reaction catalyzed with titanyl phthalocyanines in nonaqueous and aqueous media

Electrochemical and in situ spectroelectrochemical behaviors and electrocatalytic reduction of molecular oxygen with titanyl phthalocyanines (TiPc) bearing 3,4-(methylenedioxy)-phenoxy substituents were performed in aprotic solvents. Multi electrons and metal-based and ring-based redox processes of TiPcs indicate their possible electrocatalytic activity toward many target species. Different numbers and positions of the substituents of the complexes affect the peaks' character and assignment of the processes. The presence of O2 in the electrolyte system influences the electrochemical and spectral responses of TiPcs. Electrochemical and in situ spectroelectrochemical analysis indicates interaction of molecular oxygen with TiPcs and these interaction mechanisms depend on both the substituent environments of the complexes and the electrolyte system. Langmuir-Blodgett films of the complexes also catalyze molecular oxygen in aqueous media, which is a desired property for their practical application.

Evidence on the Formation of Singlet Oxygen in the Donor Side Photoinhibition of Photosystem II: EPR Spin-Trapping Study

When photosystem II (PSII) is exposed to excess light, singlet oxygen (1O2) formed by the interaction of molecular oxygen with triplet chlorophyll. Triplet chlorophyll is formed by the charge recombination of triplet radical pair 3[P680•+Pheo•−] in the acceptor-side photoinhibition of PSII. Here, we provide evidence on the formation of 1O2 in the donor side photoinhibition of PSII. Light-induced 1O2 production in Tris-treated PSII membranes was studied by electron paramagnetic resonance (EPR) spin-trapping spectroscopy, as monitored by TEMPONE EPR signal. Light-induced formation of carbon-centered radicals (R•) was observed by POBN-R adduct EPR signal. Increased oxidation of organic molecules at high pH enhanced the formation of TEMPONE and POBN-R adduct EPR signals in Tris-treated PSII membranes. Interestingly, the scavenging of R• by propyl gallate significantly suppressed 1O2. Based on our results, it is concluded that 1O2 formation correlates with R• formation on the donor side of PSII due to oxidation of organic molecules (lipids and proteins) by long-lived P680•+/TyrZ•. It is proposed here that the Russell mechanism for the recombination of two peroxyl radicals formed by the interaction of R• with molecular oxygen is a plausible mechanism for 1O2 formation in the donor side photoinhibition of PSII.

Characterization of as‐grown and adsorbate‐covered N‐polar InN surfaces using in situ photoelectron spectroscopy

AbstractThe surface electronic properties and adsorption behaviour of as‐grown and oxidized N‐polar InN films are characterized by photoelectron spectroscopy (XPS, UPS). The epitaxial growth of the InN layers was performed by plasma‐assisted molecular beam epitaxy on GaN/6H‐SiC(000‐1). After growth and in situ characterization the InN surfaces were exposed to molecular oxygen to evaluate the adsorption behaviour of O2 on N‐polar InN and to study its impact on the surface electronic properties of the III‐nitride material. The results are compared with studies on In‐polar InN on GaN/sapphire templates. The as‐grown N‐polar InN surface exhibits a pronounced surface state at a binding energy of ∼1.6 eV. The valence band minimum lies about 0.8–1.0 eV below the surface Fermi level. Additionally, the XPS core level binding energies for InN(000‐1) are reduced compared to InN(0001) films, indicating different surface band bending for clean N‐polar and In‐polar InN, respectively. The interaction of molecular oxygen with the InN(000‐1) surface leads to a downward band bending by 0.1 eV compared to the initial state. Additional adsorption of species from the residual gas of the UHV chamber increases the surface downward band bending. Furthermore two pronounced oxygen related states with an energy distance of ∼5 eV could be detected in the valence band region. The adsorbed oxygen results in an additional component in the N1s core level spectra, which is interpreted as formation of NOx bonds.

Catalytic activity toward oxygen reduction of transition metal porphyrins covalently linked to single-walled carbon nanotubes: A density functional study

The interaction of molecular oxygen with the metal center of transition metal porphyrins (MP, with M $=$ Mn, Fe, Co, and Ni) covalently linked to single-walled carbon nanotubes (CNTs) are addressed by density functional theory calculations. Two geometries for the CNT sidewall functionalization with porphyrin radicals are proposed, considering $s{p}^{2}$ and $s{p}^{3}$ chemical bonds. By computing the stability and electronic properties of the CNT-MP complexes, and the interaction of the O${}_{2}$ molecule with the metal center, we investigate their catalytic activity toward the oxygen reduction reaction (ORR). According to our results, CNT-MnP, CNT-CoP, and CNT-FeP linked by $s{p}^{2}$ covalent bonds are highly stable, preserving the CNT metallic character. We also find a significant O--O bond weakening after the oxygen adsorption on the porphyrin metal center, showing favorable conditions toward ORR. These results support experimental evidences of ORR activity in CNT-based transition metal-N${}_{4}$ centers.

Formation of Superoxide Anions on Ceria Nanoparticles by Interaction of Molecular Oxygen with Ce3+ Sites

The exposure of reduced ceria, CeO2−x, to molecular oxygen results in the formation of peroxo, O22−, and superoxo, O2−, species. The formation of diamagnetic peroxo species is easily explained by the interaction of O2 with oxygen vacancies at the ceria surface because these are two-electron-donor centers. On the contrary, the formation of the paramagnetic superoxide O2− radical cannot be explained by the same model because this complex spontaneously converts into the more stable peroxo system. On the basis of DFT calculations, we show that superoxide O2− radicals form by direct interaction of O2 with low-coordinated Ce3+ ions on reduced ceria nanoparticles and we propose an atomistic model of this system, which is fully consistent with the experimental observation.

Electrochemical and in situ spectroelectrochemical monitoring of the interaction between cobaltphthalocyanines and molecular oxygen in aprotic media

In this study, voltammetric and spectroelectrochemical measurements of cobaltphthalocyanines (CoPc) bearing different substituents were performed in aprotic solvents to determine the mechanism of interaction between CoPc and molecular oxygen. Metal-based redox processes of the cobaltphthalocyanine complexes indicate their possible electrocatalytic activities toward many target species. Different substituents of the complexes affect the peak characters and assignments of the processes. Presence of O 2 in the electrolyte system influences oxygen reduction reaction and the electrochemical and spectral behaviors of the complexes, which indicate homogeneous electrocatalytic activity of the complexes for the oxygen reduction reaction. In situ electrocolorimetric method was applied to investigate color of the anionic and cationic forms of the complexes. Electrochemical and in situ spectroelectrochemical analysis indicate interaction of molecular oxygen with monoanionic [Co IPc −2] 1− and presence of an equilibrium between the reactants [Co IPc −2] 1− and O 2 and the intermediates [ O 2 - – Co II Pc 2 - ] - and [ O 2 2 - – Co II Pc 2 - ] 2 - . This equilibrium is disturbed in desired direction by changing the excitation signals of the voltammetric and spectroelectrochemical techniques. The intermediates are very unstable, regenerating the starting form of the catalyst and the products O 2 - and O 2 2 - . Interaction rate of O 2 with the complexes is significantly influenced with the steric and coordination properties of the substituents and solvent of the system. Voltammetric and spectroelectrochemical results indicate that homogeneous electrocatalytic ORR follows an “inner sphere” chemical catalysis process.

Activation of molecular oxygen in trifluoroacetic acid

The interaction of molecular oxygen with aqueous trifluoroacetic acid (TFA) led to an increase in pH. This effect was explained by a decrease in the concentration of the protonated CF3CO2H 2 + and H3O+ species after oxygen was fed in the reactor. Quantum-chemical calculations show that a radical pair can be formed in an activation-free exothermal reaction involving the radical residue of the acid, the CF3CO2H 2 + ...3O2...CF3CO 2 − peroxide radical, and the acid molecule in the CF3C 2 · ...HOO· collision complex. It was assumed that the activation of molecular oxygen in aqueous TFA solutions, providing the activity of the system in oxidations of various organic and inorganic substrates, is related to the formation of peroxide radicals in them.