H2 DISSOCIATION ON A Pt OVERLAYER ON Ni(111)

1997 ◽  
Vol 04 (01) ◽  
pp. 45-52 ◽  
Author(s):  
N. J. CASTELLANI ◽  
C. MEHADJI ◽  
P. LÉGARÉ
Keyword(s):  
Activation Energy ◽  
Electronic Properties ◽  
Cluster Model ◽  
Molecular Adsorption ◽  
Hydrogen Atoms ◽  
Coordination Sites ◽  
Extended Hückel ◽  
Two Factors ◽  
Extended Hückel Calculations ◽  
Dissociated State

The chemisorption of hydrogen atoms and the H 2 molecule was studied by the use of extended Hückel calculations in a cluster model to simulate a Pt (111) surface and a Pt overlayer in epitaxy on Ni (111). The result of epitaxy on the chemisorptive properties of Pt is to disfavor the H atom adsorption on the higher coordination sites, and to increase the activation energy of H 2 dissociation. This is due to two factors. First, the Pt – Pt distance shortening increases the repulsion produced by the Pt neighbors on the adatoms. Second, the study of the local electronic properties of the chemisorption site shows that the pure Pt surface tends to chemisorb the H 2 molecule in the dissociated state whereas the Pt/Ni system would favor the molecular adsorption only.

A Modified Extended Hückel Calculations For Q1D-Graphites

1990 ◽  
Vol 214 ◽  
Author(s):  
D. Raković ◽  
R. Kostić ◽  
S. Krstić ◽  
I. Davidova ◽  
B. L. Fayfel ◽  
...  
Keyword(s):  
Electronic Properties ◽  
Density Of States ◽  
Computational Results ◽  
Two Dimensional ◽  
Electronic Density ◽  
Electronic Density Of States ◽  
Energy Gaps ◽  
Extended Hückel ◽  
Extended Hückel Calculations

ABSTRACTIn this paper we have computed electronic density of states for several Q1D graphites: polyacene (PA), polyacenacene (PAA), polyphenanthrene (PP), polyphenanthrophenanthrene (PPhP), and polyperinaphthalene (PPN). The modified extended Hiickel method for finite Q1D chains has been adopted. The change of the electronic properties due to the growth of the Q1D-graphites toward the two-dimensional direction, starting from trans-polyacetylene, cis-polyacetylene or poly(p-phenylene), is discussed. Our calculations show that PA, PAA, and PPN are intrinsic conductors, while PP and PPh are semiconductors with energy gaps of 1,4 eV and 0,8 eV, respectively. The comparison with other computational results is presented.

Hydrogenated Amorphous Silicon Nitride: Structural and Electronic Properties

1998 ◽  
Vol 538 ◽  
Author(s):  
J. F. Justo ◽  
F. De Brito Mota ◽  
A. Fazziom
Keyword(s):  
Silicon Nitride ◽  
Ab Initio ◽  
Amorphous Silicon ◽  
Electronic Properties ◽  
Interatomic Potential ◽  
Hydrogen Atoms ◽  
Hydrogen Incorporation ◽  
Amorphous Silicon Nitride ◽  
Structural And Electronic Properties ◽  
Hydrogenated Amorphous

AbstractWe combined empirical and ab initio methods to study structural and electronic properties of amorphous silicon nitride. For such study, we developed an interatomic potential to describe the interactions between silicon, nitrogen, and hydrogen atoms. Using this potential, we performed Monte Carlo simulations in a simulated annealing scheme to study structural properties of amorphous silicon nitride. Then this potential was used to generate relevant structures of a-SiNx:Hy which were input configurations to ab initio calculations. We investigated the electronic and structural role played by hydrogen incorporation in amorphous silicon nitride.

Electrochemical performance and electronic properties of shell LiNi0.5Mn1.5O4 hollow spheres for lithium ion battery

2016 ◽  
Vol 09 (02) ◽  
pp. 1650027 ◽  
Author(s):  
Yongli Cui ◽  
Jiali Wang ◽  
Mingzhen Wang ◽  
Quanchao Zhuang
Keyword(s):  
Activation Energy ◽  
Electrochemical Performance ◽  
Electronic Properties ◽  
Lithium Ion Battery ◽  
Retention Rate ◽  
Hollow Spheres ◽  
Lithium Ion ◽  
Reversible Capacity ◽  
Hollow Microspheres ◽  
Cycle Stability

Shell spinel LiNi[Formula: see text]Mn[Formula: see text]O4 hollow microspheres were successfully synthesized by MnCO3 template, and characterized by XRD, SEM, and TEM. The results show that the hollow LiNi[Formula: see text]Mn[Formula: see text]O4 cathode has good cycle stability to reach 124.5, 119.8, and 96.6[Formula: see text]mAh/g at 0.5, 1, and 5 C, the corresponding retention rate of 98.1%, 98.2%, and 98.0% after 50 cycles at 20[Formula: see text]C, and the reversible capacity of 94.6[Formula: see text]mAh/g can be obtained at 1 C rate at 55[Formula: see text]C, 83.3% retention after 100 cycles. As the temperature decreases from 10[Formula: see text]C to [Formula: see text]C, the resistance of [Formula: see text] increases from 5.5 [Formula: see text] to 135 [Formula: see text], [Formula: see text] from 27 [Formula: see text] to 353.2 [Formula: see text], and [Formula: see text] from 12.7 [Formula: see text] to 73.0 [Formula: see text]. Moreover, the B constant and [Formula: see text] activation energy are 4480[Formula: see text]K and 37.22[Formula: see text]KJ/mol for the NTC spinel material, respectively.

scholarly journals Extended Hückel Calculations in Spectral and Magnetic Studies of Two Distortion Isomers of Bis(1,3-diaminobutane)copper(II) Perchlorate.

1995 ◽  
Vol 49 ◽  
pp. 585-588 ◽  
Author(s):  
Rolf Uggla ◽  
Milan Melník ◽  
Jaana Valo ◽  
Aarne Pajunen ◽  
Markku R. Sundberg ◽  
...  
Keyword(s):  
Magnetic Studies ◽  
Extended Hückel ◽  
Extended Hückel Calculations

scholarly journals On the catalytic dehydrogenation of naphthenes II. Competition experiments and energies of C-H bonds

1947 ◽  
Vol 190 (1022) ◽  
pp. 309-328 ◽  
Keyword(s):  
Activation Energy ◽  
Active Sites ◽  
Catalyst Surface ◽  
Resonance Energy ◽  
Activation Energies ◽  
Theoretical Treatment ◽  
Catalytic Dehydrogenation ◽  
Simple Relationship ◽  
Hydrogen Atoms ◽  
Methyl Cyclohexane

The rates of dehydrogenation in competition experiments using mixtures of two naphthenes, or a naphthene and a cyclic mono-olefine or two cyclic mono-olefines, have been examined theoretically and experimentally for the stationary state conditions. Provided the two reactants can occupy the same sites on the catalyst surface, then the ratio of the rates should be directly proportional to the ratio of the partial pressures at any instant. Theory suggests that a constant which can be derived from these competition experiments should be independent of the overall pressures, or of the initial ratio of concentrations or of the overall extent of dehydrogenation. Further, the ratio of the rates in competition should bear no simple relationship to the ratio of the individual rates alone, but should be related to the slopes of the 1/rate against 1/pressure plot for the two components considered separately. Moreover, the constant should be a ratio of two functions each of which is characteristic of one of the naphthenes. The theoretical conclusions have been confirmed experimentally which proves either that the groups of active sites on the catalyst surface are widely separated or that any set of sites is available for the reaction of any molecular species, and no interference takes place between naphthene molecules adsorbed on adjacent sites. Proof that a naphthene and cyclohexene are dehydrogenated on the same sites is supplied by the observation that a constant is obtained when different mixtures of cyclohexene and trans -1:4-dimethyl cyclohexane are allowed to compete for the surface. The ratios for methyl, ethyl, the three dimethyl and the three trimethyl cyclohexanes in competition with cyclohexane have been accurately determined at temperatures of 400 and 450° C. From the constants so derived the activation energy differences for the removal of the first pair of hydrogen atoms has been obtained. These values are discussed in terms of the possible transition complexes, and it is shown that the reaction proceeds by the loss of a pair of hydrogen atoms simultaneously and not by a half-hydrogenated state mechanism. Using these activation energies and the experimentally found overall activation energy of 36 kcal./g. mol., the resonance energy per resonating structure was determined as 1-73 kcal. This is in good agreement with the energies of C-H bonds in alkyl radicals (2-2 kcal./g.mol./ resonating structure). The theoretical treatment suggests that the weakest C-H link in methyl cyclohexane should be in the three position to the methyl group. A study of the activation energies involved shows that the methyl cyclohexene produced from methyl cyclohexane is not 1-methyl-1-cyclohexene, thus confirming the theoretical deduction.

Water Adsorption on Ideal Anatase-TiO2(101) – An Embedded Cluster Model for Accurate Adsorption Energetics and Excited State Properties

2020 ◽  
Vol 234 (5) ◽  
pp. 813-834 ◽  
Author(s):  
Thorben Petersen ◽  
Thorsten Klüner
Keyword(s):  
Excited State ◽  
Cluster Model ◽  
Dissociative Adsorption ◽  
Molecular Adsorption ◽  
Hydrogen Electrode ◽  
Adsorption Sites ◽  
First Results ◽  
Adsorption Of Water ◽  
Hybrid Functionals ◽  
High Level

AbstractA combined theoretical approach towards the accurate description of water on anatase-TiO2(101) was pursued in this study. Firstly, periodic slab calculations on the basis of density hybrid functionals (PBE0, HSE06) were performed in order to gain insight into the adsorption sites and geometric structure of the surface. For submonolayer coverage of H2O, the molecular adsorption of water is found to be the most stable one with quite similar energetics in PBE0 and HSE06. Moreover, the transition states towards the less preferred dissociative adsorption forms are predicted to be greater than 0.7 eV. Thus, water will not spontaneously dissociate and based on the Computational Hydrogen Electrode model an overpotential of about 1.71 V is needed to drive the overall oxidation. In addition, to validate our results for molecular adsorption of H2O, an embedded cluster model is carefully evaluated for the a-TiO2(101) surface based on the periodic slab calculations. Subsequent high-level DLPNO-CCSD(T) results are in close agreement with our periodic slab calculations since the interaction is found to mainly consist of electrostatic contributions which are captured by hybrid functionals. Finally, first results on optimized geometries in the excited state based on the photogenerated charge-transfer state are presented.

THE REACTION OF HYDROGEN AND DEUTERIUM ATOMS WITH PROPANE

1939 ◽  
Vol 17b (12) ◽  
pp. 371-384 ◽  
Author(s):  
E. W. R. Steacie ◽  
N. A. D. Parlee
Keyword(s):  
Activation Energy ◽  
High Temperatures ◽  
Low Temperatures ◽  
Hydrogen Atoms ◽  
Temperature Range ◽  
Secondary Reactions

The reaction of hydrogen atoms with propane has been investigated over the temperature range 30° to 250 °C. by the Wood-Bonhoeffer method. The products are solely methane at low temperatures, and methane, ethane, and ethylene at higher temperatures.It is concluded that the results can be explained only by the assumption that the reaction[Formula: see text]is of importance. The bearing of this on the Rice-Herzfeld mechanisms is discussed. The activation energy of the reaction is 10 ± 2 Kcal.The main steps in the postulated mechanism are:Primary Reaction[Formula: see text]Secondary Reactions at Low Temperatures[Formula: see text]Additional Secondary Reactions at High Temperatures[Formula: see text]The reaction of deuterium atoms with propane was also investigated. It was found that the methane and ethane produced were highly deuterized, while the propane was not appreciably exchanged.

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