Dissociative Adsorption Of Molecular Oxygen Research Articles

Tuning the Magnetic and Catalytic Properties of Manganese Ferrite through Zn2+ Doping: Gas Phase Oxidation of Octanol

Spinel ferrites, ZnFe2O4, MnFe2O4, and ZnMnFe2O4, were synthesized using the sol–gel method and thoroughly investigated for their potential as catalytic and magnetic materials. Experiments unveiled that ZnMnFe2O4 exhibited excellent catalytic and magnetic properties, whereas the Density Functional Theory (DFT) calculations provided insight into the excellent performance of ZnMnFe2O4 compared with ZnFe2O4 and MnFe2O4. The catalytic efficiencies of the synthesized spinel ferrites were evaluated against a model reaction, i.e., the gas-phase oxidation of octanol to a corresponding aldehyde, utilizing molecular oxygen as an oxidant. The results indicated that the order of catalytic activity was ZnMnFe2O4 > MnFe2O4 > ZnFe2O4. The reaction was found to follow Langmuir Hinshelwood’s mechanism for dissociative adsorption of molecular oxygen. Owing to their superb catalytic and magnetic properties, mixed ferrites can be extended to a variety of organic transformation reactions.

CO Oxidation Efficiency and Hysteresis Behavior over Mesoporous Pd/SiO2 Catalyst

Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO2 aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO2 catalysts were investigated using carbon monoxide (CO) oxidation as a model reaction. The catalyst becomes active, and the conversion increases after the temperature reaches the ignition temperature (Tig). A normal hysteresis in carbon monoxide (CO) oxidation has been observed, where the catalysts continue to exhibit high catalytic activity (CO conversion remains at 100%) during the extinction even at temperatures lower than Tig. The catalyst was characterized using BET, TEM, XPS, TGA-DSC, and FTIR. In this work, the influence of pretreatment conditions and stability of the active sites on the catalytic activity and hysteresis is presented. The CO oxidation on the Pd/SiO2 catalyst has been attributed to the dissociative adsorption of molecular oxygen and the activation of the C-O bond, followed by diffusion of adsorbates at Tig to form CO2. Whereas, the hysteresis has been explained by the enhanced stability of the active site caused by thermal effects, pretreatment conditions, Pd-SiO2 support interaction, and PdO formation and decomposition.

Improved electrocatalytic properties of La0.3Ca0.7Fe0.7Cr0.3O3-δ electrodes for oxygen reduction reaction: The effect of electrode thickness

Three-electrode half-cells with La0.3Ca0.7Fe0.7Cr0.3O3-δ porous electrodes were prepared by screen-printing technology. The electrodes with thicknesses ranging from ∼12 to ∼62 μm exhibited similar microstructures. The electrocatalytic properties of the electrodes for oxygen reduction reaction were investigated with respect to electrode thickness. The contributions of various electrode processes to the overall electrode polarization were resolved, among which the dissociative adsorption of molecular oxygen on the surface made the most substantial contribution. A significant dependence of the electrocatalytic properties on electrode thickness was detected. Tuning electrode thickness was demonstrated to be effective in optimizing the electrocatalytic properties. The electrode with a thickness of ∼43 μm achieved the optimal electrocatalytic properties among the electrodes investigated. At 800 °C in air, this electrode showed a polarization resistance of ∼0.06 Ω⋅ cm2, an exchange current density of 797 mA⋅ cm−2 and an overpotential of 9.3 mV under an applied cathodic current density of 200 mA⋅ cm−2.

A viewpoint on catalytic origin of boron nitride in oxidative dehydrogenation of light alkanes

Oxidative dehydrogenation of light alkanes to alkenes is an attractive alternative route for industrial direct dehydrogenation because of favorable thermodynamic and kinetic characteristics, but encounters difficulties in selectivity control for alkenes because of over-oxidation reactions that produce a substantial amount of undesired carbon oxides. Recent progress has revealed that boron nitride is a highly promising catalyst in the oxidative dehydrogenation of light alkanes because of its superior selectivity for and high productivity of light alkenes, negligible formation of CO2, and remarkable catalyst stability. From this viewpoint, recent works on boron nitride in the oxidative dehydrogenations of ethane, propane, butane, and ethylbenzene are reviewed, and the emphasis of this viewpoint is placed on discussing the catalytic origin of boron nitride in oxidative dehydrogenation reactions. After analyzing recent progress in the use of boron nitride for oxidative dehydrogenation reactions and finding much new evidence, we conclude that pure boron nitride is catalytically inert, and an activation period is required under the reaction conditions; this process is accompanied by an oxygen functionalization at the edge of boron nitride; the B-O species themselves have no catalytic activity in C-H cleavage, and the B-OH groups, with the assistance of molecular oxygen, play the key role in triggering the oxidative dehydrogenation of propane; the dissociative adsorption of molecular oxygen is involved in the reaction process; and a straightforward strategy for preparing an active boron nitride catalyst with hydroxyl groups at the edges can efficiently enhance the catalytic efficacy. A new redox reaction cycle based on the B-OH sites is also proposed. Furthermore, as this is a novel catalytic system, there is an urgent need to develop new methods to optimize the catalytic performances, clarify the catalytic function of boron species in the alkane ODH reactions, and disclose the reaction mechanism under realistic reaction conditions.

Interaction of Oxygen with α-Rhombohedral Boron (001) Surface

This contribution presents a computational account of strong and exothermic interaction of atomic and molecular oxygen with the α(001)B12 surface of boron. Physisorbed oxygen interacts weakly with the surface, but the dissociative chemisorption entails considerable exothermicity in the range of 2.47–3.45 eV, depending on the adsorbed sites of the two oxygen atoms. Nonetheless, rupture of dioxygen on the surface involves a sizable intrinsic reaction barrier of 3.40 eV (at 0 K). Such high amount of energy clearly explains the chemical inertness (i.e., the lack of oxidation) of boron at room temperature. However, elevated temperature encountered in real applications of boron, such as cutting machinery, overcomes the high-energy barrier for the dissociative adsorption of molecular oxygen (3.40 eV). A stability T–P phase diagram reveals the spontaneous nature of the substitutional O/α(001)B12 adsorption modes that lead to the formation of diboron trioxide (B2O3) at temperatures and pressure pertinent to practi...

Reactivity of molecular oxygen with aluminum clusters: Density functional and Ab Initio molecular dynamics simulation study

Dissociative adsorption of molecular oxygen (O2) on aluminum (Al) clusters has attracted much interest in the field of surface science and catalysis, but theoretical predictions of the reactivity of this reaction in terms of barrier height is still challenging. In this regard, we systematically investigate the reactivity of O2 with Al clusters using density functional theory (DFT) and atom‐centered density matrix propagation (ADMP) simulations. We also calculate potential energy surfaces (PESs) of the reaction between O2 and Al clusters to estimate the barrier energy of this reaction. The M06‐2X functional gives the barrier energy in agreement with the one calculated by coupled cluster singles and doubles with perturbed triples (CCSD(T)) while the TPSSh functional significantly underestimates the barrier height. The ADMP simulation using the M06‐2X functional predicts the reactivity of O2 with the Al cluster in agreement with the experimental findings, that is, singlet O2 readily reacts with Al clusters but triplet O2 is less reactive. We found that the ability of a DFT functional to describe the charge transfer appropriately is critical for calculating the barrier energy and the reactivity of the reaction of O2 with Al clusters. The M06‐2X functional is relevant for investigating chemical reactions involving Al and O2. © 2016 Wiley Periodicals, Inc.

Chiral effect of the dissociative adsorption of molecular oxygen on the carbon nanotube surface

The electronic-energy characteristics of the adsorption of the oxygen molecule in the ground triplet and excited singlet states on the surface of chiral and achiral single-walled carbon nanotubes were studied by semiempirical MNDO and PM3 quantum-chemical methods using the molecular cluster model with boundary pseudoatoms. The energies of dissociative adsorption of molecular oxygen on the surface of nanotubes were calculated. The chiral effect of the dissociative adsorption of the O2 molecule was predicted and studied. The diameters of the carbon nanotubes that adsorb molecular oxygen most effectively were predicted. A physical rationale of the obtained dependences was presented.

Defective α-Fe2O3(0001): an ab initio study.

By using density functional theory calculations at the PBE+U level, we investigated the properties of hematite (0001) surfaces decorated with adatoms/vacancies/substituents. For the most stable surface termination over a large range of oxygen chemical potentials (muO), the vacancy formation and adsorption energies were determined as a function of muO. Under oxygen-rich conditions, all defects are metastable with respect to the ideal surface. Under oxygen-poor conditions, O vacancies and Fe adatoms become stable. Under ambient conditions, all defects are metastable; in the bulk, O vacancies form more easily than Fe vacancies, whereas at the surface the opposite is true. All defects, that is, O and Fe vacancies, Fe and Al adatoms, and Al substituents, induce important modifications to the geometry of the surface in their vicinity. Dissociative adsorption of molecular oxygen is likely to be exothermic on surfaces with Fe/Al adatoms or O vacancies.

Origin of the Energy Barrier to Chemical Reactions ofO2on Al(111): Evidence for Charge Transfer, Not Spin Selection

Dissociative adsorption of molecular oxygen on the Al(111) surface exhibits mechanistic complexity that remains surprisingly poorly understood in terms of the underlying physics. Experiments clearly indicate substantial energy barriers and a mysteriously large number of adsorbed single oxygen atoms instead of pairs. Conventional first principles quantum mechanics (density functional theory) predicts no energy barrier at all; instead, spin selection rules have been invoked to explain the barrier. In this Letter, we show that correct barriers arise naturally when embedded correlated electron wave functions are used to capture the physics of the interaction of O(2) with the metal surface. The barrier originates from an abrupt charge transfer (from metal to oxygen), which is properly treated within correlated wave function theory but not within conventional density functional theory. Our potential energy surfaces also identify oxygen atom abstraction as the dominant reaction pathway at low incident energies, consistent with measurements, and show that charge transfer occurs in a stepwise fashion.

Subsurface Oxygen on Pt(111) and Its Reactivity for CO Oxidation

Temperature has an important effect on the dissociative adsorption of molecular oxygen on platinum surfaces. Here, we show that if the substrate temperature is increased to 400–600 K, the total amount of oxygen loaded onto Pt(111) can be more than twice the well-established maximum coverage of 0.25 ML. While low energy electron diffraction and STM reveal a conventional p(2 × 2) structure of the topmost layer, temperature programmed desorption measurements indicate that additional oxygen is stored under the surface of platinum. Reactivity measurements show that this sub-surface oxygen layer does not lower the activity of such platinum surface towards CO oxidation. Therefore, while sub-surface oxygen layer does form under catalytically relevant temperatures on Pt(111), it has no great influence on the oxidizing ability of such surface. This sheds new light on the initial stages of platinum oxide formation, and may help bridge the understanding of catalytic oxidation of CO on Pt in ultra high vacuum and in high-pressure catalysis studies.

A multiscale theoretical methodology for the calculation of electrochemical observables from ab initio data: Application to the oxygen reduction reaction in a Pt(1 1 1)-based polymer electrolyte membrane fuel cell

Abstract In this work we present a multiscale theoretical methodology that scales up ab initio calculated data into elementary kinetic models in order to simulate Polymer Electrolyte Membrane Fuel Cells (PEMFC) transient operation. Detailed Density Functional Theory (DFT) calculations are performed on a model Pt(1 1 1) surface to determine the elementary kinetic rates of the Oxygen Reduction Reaction (ORR) mechanism at a Pt-based PEMFC cathode. These parameters include the effect of surface coverage on the activation barriers and are implemented into a Mean Field model describing the behavior of the electric field and charge distribution at the nanoscale interfacial vicinity to the catalyst, which is in turn coupled with microscale and mesoscale level models describing the charge and reactants and water transport phenomena across the cell. The impact of two possible ORR mechanisms on the simulated i– V curves is investigated: a first route connected with the dissociative adsorption of molecular oxygen on Pt(1 1 1), a second route related to the formation and the transformation of OOH surface species. The similarities and differences of the associated calculated i– V responses for each of these routes and the consequences on the interpretation of electrochemical observables at the cell level are discussed.

Adsorption of atomic oxygen on cubic PbTiO 3 and LaMnO 3 (001) surfaces: A density functional theory study

We present and discuss density functional theory calculations addressing the electronic structure and energetics of isolated oxygen ad-atoms at the (001) surfaces of PbTiO 3 (PTO) and LaMnO 3 (LMO) cubic perovskites. Both AO- and BO 2-type of surface terminations are considered for each perovskite. Difference electron density analysis has been carried out for each surface to probe local electronic charge redistribution upon oxygen adsorption. Our results show that the (001) surfaces of the two perovskites behave quite differently towards oxygen adsorption. In the case of the PTO (001) surfaces, the adsorbate oxygen atom was found to form a peroxide-type molecular species along with a surface lattice oxygen atom on both PbO- and TiO 2-terminated surface facets. On the other hand, the most stable oxygen adsorption site for the LMO (001) surfaces corresponds to the one expected from a natural continuation of the perovskite lattice. Moreover, the dissociative adsorption of molecular oxygen varies from being only slightly exothermic on the PTO (001) facets to being highly exothermic on the LMO (001) facets. The AO-terminated facets, in general, showed a stronger binding to the adsorbed oxygen.

Enhanced gas-sensing behaviour of Ru-doped SnO 2 surface: A periodic density functional approach

A theoretical study on Ru-doped rutile SnO 2(1 1 0) surface has been carried out by means of periodic density functional theory (DFT) at generalized gradient approximation (GGA-RPBE) level with a periodic supercell approach. Electronic structure analysis was performed based on the band structure and partial density of states. The results provide evidence that the electronic structures of SnO 2(1 1 0) surface are modified by the surface Ru dopant, in which Ru 4 d orbital are located at the edge of the band gap region. It is demonstrated that molecular oxygen adsorption characteristics on stoichiometric SnO 2(1 1 0) surface are changed from endothermic to exothermic due to the existence of surface Ru dopant. The dissociative adsorption of molecular oxygen on the Ru 5c/SnO 2(1 1 0) surface is exothermic, which indicates that Ru could act as an active site to increase the oxygen atom species on SnO 2(1 1 0) surface. Our present study reveals that the Ru dopant on surface is playing both electronic and chemical role in promoting the SnO 2 gas-sensing property.

Laser-induced diffusion of oxygen on a stepped Pt(1 1 1) surface

Laser-induced diffusion of atomic oxygen on a stepped Pt(1 1 1) surface has been studied using ultrashort pulses of near-infrared light for the generation of a hot electron distribution at the surface. The dissociative adsorption of molecular oxygen at steps on the Pt(1 1 1) surface has been used to generate a nonequilibrium distribution of an adsorbate by decorating the step edges selectively with chemisorbed atomic oxygen. The coverage at the step edges during adsorption and induced diffusion has been monitored by exploiting the sensitivity of optical second-harmonic generation (SHG) on surface symmetry, which is macroscopically broken by regular steps. The diffusion rate shows a strong nonlinear dependence on the absorbed laser fluence indicating that the diffusion process can be understood in the same framework as the well studied phenomena of desorption induced by multiple electronic transitions (DIMET). Description within an electronic friction model reveals a temperature-dependent friction coefficient which we attribute to an indirect excitation mechanism of the frustrated translations.

Lattice-gas modeling of the formation and ordering of oxygen adlayers on Pd(100)

Abstract We construct a lattice-gas (LG) model to describe not just the ordering of equilibrated adlayers of chemisorbed oxygen on Pd(1 0 0), but also the non-equilibrium ordering observed during dissociative adsorption of molecular oxygen on Pd(1 0 0). First, by combining transfer matrix analysis and Monte Carlo simulations, we determine the equilibrium phase diagrams for candidate LG models with pairwise-additive interactions including nearest-neighbor (NN) exclusion, second NN repulsion, third NN attraction, and possibly fourth NN repulsion. These interactions are selected so as to recover the p(2×2) and c(2×2) ordering observed in experiment. Interaction strengths are assessed by matching simulated and experimental phase diagrams. Second, a kinetic model is constructed to describe dissociative adsorption of molecular oxygen on second NN empty sites (consistent with NN exclusion), as well as subsequent thermally activated surface diffusion, and adlayer formation. Hopping rates for the latter reflect the selected adspecies interactions through detailed-balance constraints. By comparing simulated diffracted intensities for non-equilibrium adlayer structure during adsorption with experimental data for various temperatures and pressures, we demonstrate the existence of transient mobility for dissociative adsorption in this system, and also determine the magnitude of the thermal diffusion barrier.

Periodic Density Functional Theory Study of the Dissociative Adsorption of Molecular Oxygen over La2O3.

Results of spin-polarized, gradient-corrected, periodic density functional theory calculations are reported for the dissociative adsorption of molecular oxygen over the oxide surface of La2O3(001). The diatomic surface oxygen species formed from O2 dissociation are characterized structurally by a bent orientation with respect to the surface and an OsurfaceO bond length of 1.47 A; both attributes are consistent with structural features characteristic of classical peroxides. The overall reaction energy for O2 dissociation into surface peroxide species was calculated to be endothermic by only 12.1 kcal/mol. Several reaction pathways leading to the product were examined; the lowest energy path identified involves a three-center transition state and has an apparent activation barrier of 33.0 kcal/mol. We comment on the role that peroxide species may play in the CH bond activation step of catalytic oxidative coupling of methane.

Periodic Density Functional Theory Study of the Dissociative Adsorption of Molecular Oxygen over La2O3

Results of spin-polarized, gradient-corrected, periodic density functional theory calculations are reported for the dissociative adsorption of molecular oxygen over the oxide surface of La2O3(001). The diatomic surface oxygen species formed from O2 dissociation are characterized structurally by a bent orientation with respect to the surface and an OsurfaceO bond length of 1.47 A; both attributes are consistent with structural features characteristic of classical peroxides. The overall reaction energy for O2 dissociation into surface peroxide species was calculated to be endothermic by only 12.1 kcal/mol. Several reaction pathways leading to the product were examined; the lowest energy path identified involves a three-center transition state and has an apparent activation barrier of 33.0 kcal/mol. We comment on the role that peroxide species may play in the CH bond activation step of catalytic oxidative coupling of methane.

Catalytic ignition of methane/oxygen mixtures over platinum surfaces: comparison of detailed simulations and experiments

The surface ignition of methane/oxygen/nitrogen mixtures over a platinum foil is modeled at atmospheric pressure with a revised detailed surface kinetics mechanism including 20 surface reactions and seven surface species, detailed gas-phase kinetics and simplified multicomponent transport. Simulation results are compared to experimental data from the literature and very good agreement is found. Sensitivity analysis shows that the dissociative adsorption of molecular oxygen and the decomposition of methane are the most important steps in affecting the catalyst ignition. Comparison with experiments and sensitivity analysis indicate that methane adsorption is activated, and contrary to previous suggestions, partial equilibrium in adsorption/desorption steps breaks down. In addition, prior to ignition the adsorption of reactants is competitive and combustion products are favored as compared to syngas. Finally, results are compared to hydrogen/air mixtures.

The influence of OH − chemisorption on the catalytic properties of gold single crystal surfaces for oxygen reduction in alkaline solutions

Oxygen reduction on gold single crystal electrodes of various orientations, Au( hkl), in 0.1 M NaOH was studied by rotating disk electrode and rotating disk ring electrode techniques, with a goal to correlate the physical and chemical properties of the electrode surface with its catalytic activity. The characterization of the state of the electrode surface and the interface was carried out by cyclic voltammetry and differential capacity measurements. The geometrical arrangement and symmetry of surface atoms, and the presence of chemisorbed OH − anions, were found to play a key role in determining the catalytic properties of Au( hkl) surfaces for O 2 reduction. It was proposed that chemisorbed anions act as a precursor for the dissociative adsorption of molecular oxygen or for chemisorption of reaction intermediate, catalyzing the 4e −-reduction of O 2.

A quantum-chemical MINDO/3 study of methane and oxygen interactions with a pure and a modified calcium oxide surface

Within the framework of theMINDO/3 method methane and oxygen interactions with pure and modified calcium oxide have been considered. It is shown that low-coordinated Ca 2+ 3C-O 2− 4C and Ca 2+ 4C-O 2− 3C pairs of acid-base centers are responsible for the initial step in the methane activation on pure calcium oxide. Atomic oxygen strongly adsorbs only on surface basic sites yielding surface O 2− 2 species. Molecular oxygen adsorbs both on acid and basic sites and forms either π-complexes or O 3 species, respectively. However, the dissociative adsorption of molecular oxygen on adjacent pairs of basic sites is energetically more favorable. The energetics of the substitution of a Ca 2+ LC ion by Mg 2+ LC in Mg/CaO, Na + LC in Na/CaO and Zn 2+ LC in Zn/CaO and Na/Zn/CaO and the methane activation on these modified calcium oxides have also been considered. The results allow an understanding of the experimentally observed increase of the C 2+ hydrocarbon selectivity in the oxidative coupling of methane both on mixed magnesium and calcium oxides containing 10 to 15% of CaO and on NaOH-promoted CaO catalysts containing minor amounts of Zn 2+ cations.