arXiv subjects

Zhenjun Song

Publications and source records attributed to Zhenjun Song.

7 recordsLinked to original sources

arXiv2017

Homolytic Cleavage of Water on Magnesia Film Promoted by Interfacial Oxide-Metal Nanocomposite

The atomic scale insights into the interaction of water with oxide surface are essential for elucidating the mechanism of physiochemical processes in various scientific and practical fields, since the water is ubiquitous and coats multifarious material surface under ambient conditions. By utilizing periodic density functional theory calculations with van der Waals corrections, herein we report for the first time the energetically and thermodynamically favorable homolytic dissociative adsorption behavior of water over magnesia (001) films deposited on metal substrate. The water adsorption on pristine magnesia (001) is quite weak and the heterolytic dissociation is the only fragmentation pathway, which is highly endothermic with large activation barrier of 1.167 eV. The binding strength for the molecular and dissociative adsorption configurations of water on hybrid MgO(001) films are significantly larger than corresponding configurations on bare magnesia (001). The homolytic dissociative adsorption energy of water on monolayer oxide is calculated to be -1.192 eV, which is even larger than all the heterolytic dissociative adsorption states. With the increase of the oxide thickness, the homolytic dissociative adsorption energy decreases promptly, indicating the nanoscale of oxide film play a crucial role in homolytic splitting of water. The homolytic dissociative adsorption structure could be obtained by transformation reaction from heterolytic dissociative adsorption structure, presenting activation barriers 0.733, 1.103, 1.306, 1.571, and 1.849 eV for reactions on 1 ML to 5 ML films. It is anticipated that the results here could provide inspiring clue and versatile strategy for enhancing chemical reactivity and properties of insulating oxide toward homolytic water splitting processes involved in novel and unprecedented applications.

physics.chem-ph↗

arXiv2017

Remarkably strong chemisorption of nitric oxide on insulating oxide films promoted by hybrid structure

The remarkably strong chemical adsorption behaviors of nitric oxide on magnesia (001) film deposited on metal substrate have been investigated by employing periodic density functional calculations with Van der Waals corrections. The molybdenum supported magnesia (001) show significantly enhanced adsorption properties and the nitric oxide is chemisorbed strongly and preferably trapped in flat adsorption configuration on metal supported oxide film, due to the substantially large adsorption energies and transformation barriers. The analysis of Bader charges, projected density of states, differential charge densities, electron localization function, highest occupied orbital and particular orbital with largest Mg-NO-Mg bonding coefficients, are applied to reveal the electronic adsorption properties and characteristics of bonding between nitric oxide and surface as well as the bonding within the hybrid structure. The strong chemical binding of nitric oxide on magnesia deposited on molybdenum slab offers new opportunities for toxic gas detection and treatment. We anticipate that hybrid structure promoted remarkable chemical adsorption of nitric oxide on magnesia in this study will provide versatile strategy for enhancing chemical reactivity and properties of insulating oxide.

physics.chem-ph↗

arXiv2016

Unique catalytic decomposition and reduction of hydrogen peroxide and organic peroxides on magnesia (001) promoted by oxide-metal hybrid nanostructure

The detection, removal and reduction of hydrogen peroxide is of significant importance for its increasing application in the areas of environment, food, electrochemistry and clinical laboratory. Herein the dissociative adsorption behavior of hydrogen peroxide on ultrathin magnesia (001) films deposited on transition metal is uncovered for the first time by employing periodic density-functional theory calculations with van der Waals corrections. The hydrogen peroxide is dissociated smoothly and reduced to surface hydroxyls on MgO(001)/TM, and the dissociative adsorption energies of all the considered fragmentation configurations are substantially negative, demonstrating dissociation and reduction of hydrogen peroxide on MgO(001)/TM is thermodynamically favorable. The dissociative adsorption energy decreases monotonously with increasing film thickness, demonstrating the lower reactivity of thick oxide films. Moreover, we examined the suitability of several transition metal slabs (molybdenum, silver, vanadium, tungsten and gold) combined with magnesia for splitting hydrogen peroxide. The dissociative adsorption energies enhance when the lattice constants of substrate slabs increase, indicating the chemisorption strength can be tuned by category of metal slabs as well as thickness of oxide film. The mechanism of reactivity enhancement for energetically and dynamically favorable decomposition of hydrogen peroxide on supported magnesia is elucidated by characterizing the geometric structures and electronic properties. The fragmentation and reduction of diethyl peroxide and peroxyacetone are also studied to reveal the catalytic activity of ultrathin magnesia toward splitting organic peroxides. The results are wished to provide useful clue for detecting and reducing hydrogen peroxide and organic peroxides by employing oxide-metal hybrid nanostructure.

physics.chem-ph↗

arXiv2016

Spontaneous dehydrogenation of methanol over defect-free MgO(100) thin film deposited on molybdenum

The dehydrogenation reaction of methanol on metal supported MgO(100) films has been studied by employing periodic density functional calculations. As far as we know, the dehydrogenation of single methanol molecule over inert oxide insulators such as MgO has never been realized before without the introduction of defects and low coordinated atoms. By depositing the very thin oxide films on Mo substrate we have successfully obtained the dissociative state of methanol. The dehydrogenation reaction is energetically exothermic and nearly barrierless. The metal supported thin oxide films studied here provide a versatile approach to enhance the activity and properties of oxides.

physics.chem-ph↗

arXiv2015

Unusual dissociative adsorption of H2 over stoichiometric MgO thin film supported on molybdenum

The dissociation of a hydrogen molecule on MgO(001) films deposited on Mo(001) surface is investigated systematically using periodic density-functional theory method. The unusual adsorption behavior of heterolytic dissociative hydrogen molecule at neighboring surface oxygen and surface magnesium, is clarified here. To my knowledge, this heterolytic dissociative state has never been found before on bulk MgO(001) or metal supported MgO(001) surfaces. The results confirm that, in all cases, the heterolytic dissociation is much more favorable that homolytic dissociation both energetically and kinetically. The energy difference between two dissociative states are very large, in the range of 1.1 eV ~ 1.5 eV for Mo supported 1 ML ~ 3 ML oxide films, which inhibits, to a great extent, the homolytic dissociation in the respect of reaction thermodynamics. The energy barrier of heterolytic dissociation are about 0.5 eV, much lower that the barrier of homolytic dissociation. The transformation reaction on thick films will be more endothermic. Passing through heterolytic dissociation state have significantly lowered the reaction heat and the energy barrier for obtaining homolytic dissociative structure, which make the homolytic splitting of H2 easier on 2 ML oxide films. The results provides a useful strategy for enhancing the reactivity of the nonreducible metal oxide.

physics.chem-ph↗

arXiv2015

Strain-Induced Water Dissociation on Supported Ultrathin Oxide Films

Controlling the dissociation of single water molecule on an insulating surface plays a crucial role in many catalytic reactions. In this Letter, we have identified the enhanced chemical reactivity of ultrathin MgO(100) films deposited on Mo(100) substrate that causes water dissociation. We reveal that the ability to split water on insulating surface closely depends on the lattice mismatch between ultrathin films and the underlying substrate, and substrate-induced in-plane tensile strain dramatically results in water dissociation on MgO(100). Three dissociative adsorption configurations of water with lower energy are predicted, and the structural transition going from molecular form to dissociative form is almost barrierless. Our results provide an effective avenue to achieve water dissociation at the single-molecule level and shed light on how to tune the chemical reactions of insulating surfaces by choosing the suitable substrates.

physics.chem-ph↗

arXiv2015

Generation of highly reactive oxygen species by co-adsorption of oxygen and water on metal-supported MgO(100) thinfilms

The formation of highly reactive oxygen species (ROS) on metal oxide surfaces have attracted considerable interest due to their diverse applications. In this work, we have performed densi-ty-functional theory calculations to investigate the co-adsorption of oxygen and water on ul-trathin MgO(100) films deposited on Mo(100) substrate. We reveal that the molecular oxygen can be stepwise decomposed completely with the assistance of water. Consequently, a series of highly ROS including superoxide, hydroperoxide, hydroxyl and single oxygen adatom are formed on Mo(100) supported MgO(100) thinfilms. The reaction barriers accompanied by the generation of ROS are reported, and the influence of the thickness of MgO(100) films is also discussed. The most promising routes to produce these fascinating species provide valuable information to understand the importance of synergistic effect, namely the substrate, the co-adorbed species, and the film thickness, in multiphase catalyst design.

physics.chem-ph↗