Search

The surface structures and segregation of ultrathin polystyrene (PS)

The intercrystalline migration of aromatic molecules adsorbed in zeolites is investigated. It is shown that the fluorescence microscopy is advantageous than the spectroscopic method.

The physisorption and chemisorption of some n-hydrocarbons are studied. It is shown that the relative stability of protonated hydrocarbons depends on the length of the molecule.

The adsorption of H2 molecules on the (100) MoS2 surfaces, considering various edge sulfur stoichiometries is investigated theoretically, by quantum density functional theory (DFT) calculations. A thermodynamic diagram is constructed by using the adsorption energies, which gives the stoichiometry of the edges and the nature of the adsorbed hydrogen atoms as a function of the total pressure.

A series of quantum mechanics calculations on uranyl and Sr2+ complexes of O=PR3 ligands (R = H, methyl, phenyl) is presented. The study aims to determine the role of substituents R and of NO3(super 1-) counterions on the intrinsic cation-ligand interaction energy. The results showed that the binding sequence of UO2(super 2+) and Sr2+ complexes were H < methyl < phenyl in the absence of counterions. The OPMe3 and OPPh3 complexes exhibited similar stability in the presence NO3(super -) counterions.

Phase transitions in the hydrogen bond subsystem of associating fluids are discussed in the framework of mean-field theory. It is presented that in the simplest case of independent bonds the free energy of the subsystem as a function of the numbers of hydrogen bonds is convex.

A numerical method is used to characterize the steady-state voltammetry at microdisk electrodes of a new electrocatalytic reaction. The numerical method for simulating this reaction scheme is based on the finite-difference formulation of coupled mass transport and kinetic equations in oblate spherical coordinates.

The expressions for density and fraction of hydrogen-bonding and hydrogen atoms are derived and applied from supercooled to superheated states of liquid water. The anomalous density variation (around 4 degree Celsius) with temperature is explained solely on the basis of hydrogen-bonding and non-hydrogen-bonding hydrogen atoms in the liquid.

The properties of two types of surface of OH species, terminal and bridged, as well as corresponding vacant sites on zirconium hydroxide at 573 K are studied using dimetyl ether adsoprtion as an IR molecular probe. The preferential reaction of acidic carbon dioxide with the t-OH group demonstrated that the t-OH group acts as a base, in which t-OH oxygen lone pairs are favorable in the electrophilic reaction.

A group definition criterion based on Bader's theory of atoms in molecules is used to characterize functional group in 1-alkanols. The experimental study of the thermophysical properties of liquid mixtures containing organic compounds has aroused a high interest in recent times on account of their impact on industry and technology.

Catalytic activity for oxygen electroreduction in acidic medium has been studied. Catalysts have been produced by pyrolyzing perylene tetracarboxylic dianhydride combined with Fe and nitrogen precursors.

The effect of photoexcitation of the adsorbed species on the electronic properties of the surface is investigated applying wavelength and time dependent two-photon photoemission spectroscopy. The conclusion states that photoexcitation of a small fraction of the weakly bound RB species causes a significant change in the electronic properties of the substrate.

The stability of the (100) molybdenum sulfide surface is studied using periodic DFT calculations taking into account various parameters such as temperature and the partial pressure ratios of hydrogen and hydrogen sulfide present in the surrounding atmosphere. Hydrodesufurization is the most important catalytic process used to remove sulfur from petroleum fractions.

Silylium cations undergo dissociative ion/surface reactions in the course of low-energy collisions with hydroxyl-terminated, hydrocarbon and fluorocarbon elf-assembled monolayer surfaces. Thermodynamic estimates regarding charge exchange between the surface and the projectile ion are consistent with the relative amounts of chemically sputtered products observed for each of the surfaces.

Chemistry research is presented describing the study of methanol catalyzed Toluene mixed with acidic mordenite to determine alkylate reactions.

The adsorption of benzene in pure-silica and acid mordenite has been investigated using density functional theory, both in the local density approximation and including generalized-gradient corrections. Benzene acts as a test molecule for studying the interaction between an aromatic hydrocarbon and a zeolite. Different adsorption modes have been studied for several acid sites. All configurations have been optimized by minimizing the total energy with respect to all lattice parameters and to the atomic coordinates. The strength of the adsorption is directly correlated to the local structural distortion of the zeolitic framework, especially of the acid site. Only if strong adsorption occurs, the molecule itself is slightly deformed. Furthermore, an analysis of the differential charges has been performed, indicating substantial polarization effects for the acid site as well as for the molecule. Finally, the red-shift of the OH-stretching frequencies due to the adsorption has been calculated. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A periodic density functional theory (DFT) study of the isomerization reactions of toluene and xylene catalyzed by acidic mordenite is reported. Monomolecular isomerization reactions have been considered and analyzed. The different reaction pathways have been discussed in detail. The use of periodic structure calculations allows consideration and analysis of zeolite electrostatic contributions and steric constraints that occur within zeolite micropores. Major differences in the details of protonation reaction pathways are found when periodic structures are used rather than small cluster models of the Brønsted acidic site. Complex relationships are found between zeolite topology and reaction pathways.

A theoretical study of the alkylation reaction of toluene with methanol catalyzed by the acidic Mordenite (Si/Al = 23) is reported. Cluster DFT as well as periodical structure DFT calculations have been performed. Full reaction energy diagrams of the elementary reaction steps that lead to the formation of the three xylene isomers are given. The use of periodical structure calculations allows one to account for zeolite framework electrostatic contributions and steric constraints that take place in zeolitic catalysts. Especially the steric constraint energy contribution has a significant effect on the energies and bond formation paths. The activation energy barrier of p-xylene formation is found to be approximately 20 kJ/mol lower than the corresponding values for the formation of its isomers. Computed host-guest binding energies according to the DFT method need a correction due to the absence of the dispersive interaction with the zeolite wall. Apparent activation energies obtained with this correction are in good agreement with experimental data.