共查询到20条相似文献,搜索用时 31 毫秒
1.
V. Yu. Bychkov Yu. P. Tulenin M. M. Slinko D. N. Vturina V. N. Korchak 《Russian Journal of Physical Chemistry B, Focus on Physics》2018,12(5):830-835
Self-oscillations of the rate of oxidation reactions of CO and CH4 on nickel foil are compared. It has been shown that, despite significant differences in the stepwise mechanism of the two reactions, the properties of oscillation regimes are very close. In both reactions, oscillation regimes result from oxidation and reduction of nickel and are accompanied by wave processes on the catalyst surface. The similarity in the properties of rate oscillations in the reactions of CO and CH4 oxidation shows that a change in the selectivity and the formation of carbon on the nickel surface are not key factors in the mechanism of the rate oscillations in CH4 oxidation. An observed periodic change in the concentrations of reactants and reaction products when the reaction mixture is supplied in a pulse mode proves that, in both cases, the self-oscillations of the reaction rate are due only to the reaction mechanism and are not caused by a change in the catalyst temperature. 相似文献
2.
V. Golovanov M. Viitala T. Kortelainen O. Cramariuc T.T. Rantala 《Surface science》2010,604(19-20):1784-1790
Siloxane is a favorable candidate as an anchor group that can be used to bind organic molecules to SnO2 surfaces, with a wide range of practical applications. Therefore, adsorption geometries and energies of siloxane coupler on the SnO2 (110) surface have been investigated in this study using quantum-chemical periodic density functional theory (DFT) calculations. We present a comparative study of different siloxane adsorption arrangements on pristine and fluorine doped SnO2 surface. According to the calculations, the surface doping with fluorine leads to stabilization of the siloxane network at the stannic oxide surface. The trend is analyzed in terms of additional charge provided by F impurities to the chemisorbed oxygen atoms thus increasing the ionicity of their bonding. Implications of the current findings for the design of organic-metal oxide interface with better thermo-stability and improved electronic properties are discussed. 相似文献
3.
A. V. Maiorov B. E. Krisyuk A. A. Popov 《Russian Journal of Physical Chemistry B, Focus on Physics》2008,2(5):707-710
The initial stage of the reaction between ozone and hexafluoropropylene (HFP) was studied by the DFT/B3LYP quantum-chemical method using the family of 6-31G basis sets and the cc-pVDZ+ basis set. Two reaction paths were compared, concerted (the Criegee mechanism) and nonconcerted (the DeMore mechanism) addition. For both reaction paths, the geometry and transition state energies, entropy, and thermodynamic and electronic enthalpy were calculated and the rate constants of the reaction were estimated. It was shown that the DeMore mechanism should be given preference for the reaction of HFP with ozone. UB3LYP calculations for the DeMore mechanism give reaction rate constants close to the experimental values. 相似文献
4.
因在温室气体的降解中扮演重要的角色,通过改性来提高二氧化钛的光催化性能的相关研究备受关注.由于催化反应主要发生在材料表面,因此对材料表面的改性研究尤为重要.本文采用第一性原理方法计算了金属Ag,Cu单掺杂及协同掺杂TiO_2(001)和(101)表面不同位置,通过形成能的比较获得了最稳定的晶体结构.通过对能带及态密度的对比得出:离子掺杂(001)表面所形成的活性基团的氧化性较(101)面更强,利于光催化氧化性能的提升;表面协同掺杂较单掺杂具有更强的光响应效率,与前人的实验结果符合较好. 相似文献
5.
Heterogeneous reactions are chemical reactions that occur at the interfaces of multiple phases, and often show a nonlinear dynamical behavior due to the effect of the time-variant surface area with complex reaction mechanisms. It is important to specify the kinetics of heterogeneous reactions in order to elucidate the microscopic elementary processes and predict the macroscopic future evolution of the system. In this study, we propose a data-driven method based on a sparse modeling algorithm and sequential Monte Carlo algorithm for simultaneously extracting substantial reaction terms and surface models from a number of candidates by using partial observation data. We introduce a sparse modeling approach with non-uniform sparsity levels in order to accurately estimate rate constants, and the sequential Monte Carlo algorithm is employed to estimate time courses of multi-dimensional hidden variables. The results estimated using the proposed method show that the rate constants of dissolution and precipitation reactions that are typical examples of surface heterogeneous reactions, necessary surface models, and reaction terms underlying observable data were successfully estimated from only observable temporal changes in the concentration of the dissolved intermediate products. 相似文献
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7.
Current development of the research of radiation damage in ionic solids is reviewed. Emphasis is placed on the correlation between elementary radiation damage processes and the atomic and electronic structures of the materials. Both the radiation damage induced by electronic excitation and by elastic collision are treated. For the former two crucial processes, the self-trapping of excitons and the formation of stable Frenkel pairs from the self-trapped excitons in several materials, is discussed in terms of the structures of materials. Deficiency in the available data on the knock-on threshold energies are pointed out. Available information of Frenkel pairs produced by electronic and elastic encounters is surveyed. Possible models of defect clustering are summarized and existing information on clustering is discussed on their basis. 相似文献
8.
I. V. Zaporotskova E. V. Prokof’eva 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(3):530-536
The electron-energy characteristics of the saturation of the cavity of carbon nanotubes of armchair and zig-zag types with
molecular hydrogen are theoretically studied. The calculations are performed based on a model of a molecular cluster with
the use of the MNDO and PM3 methods, which proved to be effective in predicting the electronic structure of molecules and
periodic solids. Two mechanism of saturation of the cavity of single-walled carbon tubulenes with hydrogen molecules were
proposed and examined: (1) the mechanism of surface wetting and (2) the capillary mechanism of filling. 相似文献
9.
S.Roy Morrison 《Surface science》1975,50(2):329-342
It is shown that present models of Lewis acidity or basicity and of surface states on ionic solids have substantial overlap, although the former is designed to describe chemical interactions at the surface site, and the latter electron capture. The site requirements for a Lewis acid are compared to the requirements for an acceptor surface state to suggest under what conditions a site should exhibit both strong acidity and a deep surface state: The expected influence of electronic properties of the solid on acid strength, and the influence of adsorbed water, acids or bases on surface state energies are discussed. Experimental measurements are reported where both chemical acidity measurements and electrical surface state measurements are made on a series of Lewis acids. A positive correlation is found. Where there is correlation, it is concluded that chemical interaction measurements should provide a valuable tool to describe the energy distribution of surface states on a semiconductor surface. Also, the use of the surface state models and measurements from semi-conductor physics should help in understanding and classifying acid and basic sites on ionic semiconductors and insulators. 相似文献
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11.
L. A. Rebane A. A. Gorokhovskii J. V. Kikas 《Applied physics. B, Lasers and optics》1982,29(4):235-250
Characteristic features of photochemical hole-burning (PHB) in the impurity spectra of low-temperature solids and PHB applications in molecular spectroscopy are considered. The evolution of a no-phonon hole and a phonon sidehole in excitation and fluorescence spectra is analysed on the basis of model calculations. Some more complex models for PHB are considered, which take into account reverse reactions, the optical thickness of the sample, the inhomogeneous dispersion of both homogeneous linewidths and transition energies of the photoproduct and quasi-static impurity-impurity interactions. The effects of PHB on fluorescence line narrowing are discussed. By PHB homogeneous linewidths of purely electronic and vibronic no-phonon lines in the spectra of some porphine and phthalocyanine derivatives in various matrices are measured and their temperature dependence is studied. The latter is found to be essentially different in polycrystalline and glassy matrices. Line-broadening mechanisms are discussed. By PHB the existence of an inhomogeneous distribution of vibrational frequencies in molecular impurities is established. The applications of PHB in the studies of photochemical reactions in solid solutions of phthalocyanine derivatives and tetracene are regarded and the mechanisms of these reactions are discussed. The results obtained by PHB for chlorophyll and its derivatives are presented. 相似文献
12.
J. R. B. Gomes S. Gonzalez D. Torres F. Illas 《Russian Journal of Physical Chemistry B, Focus on Physics》2007,1(4):292-306
The study of the molecular mechanism of chemical reactions occurring at solid surfaces is of primary importance to understand
heterogeneous catalysis from a microscopic point of view. The present paper reviews the state of the art methods of electronic
structure and the surface models currently used in this type of studies by making use of three different examples. Those are
the decomposition of azomethane on Pt(111), the study of the different selectivity of Cu(111) and Ag(111) towards ethene partial
oxidation and the comparative study of NO dissociation on Rh(111) and bimetallic RhCu(111) surfaces. These examples illustrate
the power of the electronic structure computational approaches to predict the structure and stability of different intermediates
and to unravel the molecular mechanism of these surface reactions. 相似文献
13.
Frontal propagation of a highly exothermic polymerization reaction in a liquid is studied with the goal of developing a mathematical model of the process. As a model case we consider monomers such as methacrylic acid and n-butyl acrylate with peroxide initiators, although the model is not limited to these reactants and can be applied to any system with the similar basic polymerization mechanism. A three-step reaction mechanism, including initiation, propagation and termination steps, as well as a more simple one-step mechanism, were considered. For the one-step mechanism the loss of stability of propagating front was observed as a sequence of period doubling bifurcations of the front velocity. It was shown that the one-step model cannot account for less than 100% conversion and product inhomogeneities as a result of front instability, therefore the three-step mechanism was exploited. The phenomenon of superadiabatic combustion temperature was observed beyond the Hopf bifurcation point for both kinetic schemes and supported by the experimental measurements. One- and two-dimensional numerical simulations were performed to observe various planar and nonplanar periodic modes, and the results for different kinetic schemes were compared. It was found that stability of the frontal mode for a one-step reaction mechanism does not differ for 1-D and 2-D cases. For the three-step reaction mechanism 2-D solutions turned out to be more stable with respect to the appearance of nonplanar periodic modes than corresponding 1-D solutions. Higher Zeldovich numbers (i.e., higher effective activation energies or lower initial temperatures) are necessary for the existence of planar and nonplanar periodic modes in the 2-D reactor with walls than in the 1-D case. (c) 1997 American Institute of Physics. 相似文献
14.
KOICHI HASEGAWA KENTARO DOI KOICHI NAKAMURA AKITOMO TACHIBANA 《Molecular physics》2013,111(1-2):295-307
Surface crossing of the potential energy surfaces (PESs) and the formulation of differentiable PES functions are discussed in the quartet N+ 2 + O2 system containing the T shape intermediate complex. Consideration of the ion-dipole interaction between N2 and O2 fragments due to the induced dipole moment of the neutral molecule gives a good image of the surface crossing between the quartet reactant state (N+ 2 ···O2) and the quartet product state (N2 ···O+ 2) for the charge transfer (CT) reaction in terms of the conventional harpooning mechanism. Differentiable functions of PESs are constructed for the reactant and product states that may be applied for 3-dimensional dynamics calculations by means of wavepackets, and examples of 2-dimensional wavepacket dynamics calculations are introduced. Further, electron transfer processes and local electronic nature in the CT reaction are discussed in terms of the quantum mechanical energy densities based on regional density functional theory. Regional partitioning by using the kinetic energy density provides a new concept of electron transfer, and the tension density provides new images of microscopic electronic stresses. 相似文献
15.
C.B. Duke 《Surface science》1978,70(1):674-691
A brief review is given of the present state of knowledge of the surface properties of polymers and molecular solids. These materials are shown to exhibit surface phenomena which are dramatically different from those characteristic of metals and covalent solids. The origin of these differences resides in the combined occurrence both of large electronic and atomic polarizabilities and of small probabilities for the transfer of an electronic excitation from one molecular site to another. The interplay of these two quantities leads to a diversity in the character of the resulting electronic excitations, ranging from localized molecular ion states in aromatic pendant-group polymers to quasi-one-dimensional metallic behavior in certain charge transfer salts and polymers. The primary role of the surface in such materials is the introduction of large, inhomogeneous fluctuations in the relaxation energies associated with the polarization of the solid by an excitation. These fluctuations produce a number of novel phenomena including localized surface states in the absence of dangling bonds, inhomogeneous broadening of photo-emission spectra, and alterations of the charge state of surface molecules. A simple, unified theoretical framework is developed for the interpretation of these phenomena. 相似文献
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Rebecca K. Carlson Rachel A. Lee Jed H. Assam Megan L. Nagel 《Molecular physics》2015,113(13-14):1809-1822
We report the results of a joint theoretical and experimental investigation into the copolymerisation of acrylamides and acrylates with α-olefins in free-radical processes. The transition-state structures of models for free-radical homo- and copolymerisation involving acrylamide, methylacrylamide, methacrylate, methyl methacrylate, and ethylene have been determined using density functional theory. The reaction energies and barrier heights comport with the experimentally observed properties, including the prevalence of monomer alternation, the realised stereospecificity, and the reaction yield. Continuum solvation models have been applied to determine the sensitivity of the relative energies to the bulk solvent properties. Experimentally, a Lewis acid catalyst is demonstrated to increase the incorporation of nonpolar 1-alkenes in copolymerisations with polar acrylamides and acrylates. In the presence of the Lewis acid, scandium (III) trifluoromethanesulfonate, the copolymerisation of 1-hexene and acrylamide results in an 8.5 mol % incorporation, up from 3.9 mol % in the absence of the Lewis acid. Computations incorporating Mg2+ as a model Lewis acid elucidate the mechanism of this catalysis. In the addition of methacrylate to a methyl methacrylate radical terminated polymer, the Lewis acid binds to the carbonyls on both promoting isotactic addition, while for the addition of an alkene to the same polymer, the Lewis acid binds to the polymer, reducing the barrier for alkenyl addition inductively by withdrawing electron density. We have demonstrated the ability of computational studies to aid experimentalists in the synthesis of new copolymers with desired properties. 相似文献
18.
I.S Gurbanovich E.Zh Magzumov V.G Neudatchin E.A Romanovsky Yu.M Tchuvilsky 《Annals of Physics》1974,87(2):263-288
The present work contains the analysis of various reactions proceeding at relatively small projectile energies (~ 10 MeV) for which a mechanism described by the square diagram may be regarded as a dominant one. It is shown that such a mechanism may be realized both in reactions in which one or several nucleons are transferred and in reactions of nucleon or deutron inelastic scattering. Also, such an interesting property of the above diagrams is discussed as the extremely well pronounced forwardness of the angular distributions for the processes of inelastic scattering. Various variants of the theory are examined (DWBA, oscillator approximation, etc.). Formal properties of the square diagrams are also studied such as the dependence of differential cross section shape on the value of total orbital momentum transferred and the approximation on an energy surface for its calculation. 相似文献
19.
A.M. Stoneham 《物理学进展》2013,62(4):457-492
Most studies of imperfect solids concentrate on the properties of individual isolated defects. These include electronic structure, formation energies and diffusion parameters of point defects and point defect aggregates. Many physical phenomena are determined by defect processes, in which defects interact or the defect state of the lattice evolves. Such phenomena include the radiation damage process and subsequent development of microstructure, the matter and charge transport in the growth of oxide films, the recombination—or ionization—assisted diffusion in many systems, and a range of degradation mechanisms. These and other examples are discussed. The emphasis is on those cases where quantitative theory can unravel phenomena which experiment alone cannot easily do, notably those situations where the time scales are inconvenient or the system too complex for easy experimental analysis. 相似文献
20.
The surface of charged wet TiO2 anatase (001) functionalised by ruthenium ion at ambient temperatures is studied by computational modelling. Response of this model to photoexcitations at ambient temperatures is explored with the Redfield density matrix equation of motion on the basis of Kohn–Sham orbitals. The parameters of the Redfield equation are on-the-fly non-adiabatic couplings for electronic degrees of freedom obtained along the ab initio molecular dynamics nuclear trajectories. The main results in this study are the following: (1) optical properties of the doped models such as light absorption intensity and transition energies can be tuned by modifying total charge; (2) electron and hole relaxation rates depend on the initial excitation; and (3) in the doped model, excitations of lower energy provide quicker relaxation. Results of computational modelling would benefit understanding of the mechanism of electron transfer processes on the surface of ruthenium-doped TiO2. 相似文献