S. N. Lanin

Selective hydrogenation of phenylacetylene into styrene on gold nanoparticles

Gold nanoparticles (2–10 nm) supported on γ-Al2O3 exhibit high activity and stability in the hydrogenation of phenylacetylene into styrene in the phenylacetylene-styrene mixture. The selectivity of the catalyst is particle size-dependent: the styrene-to-ethylbenzene molar ratio in the reaction products increases from 2 to 30 as the average gold particle size decreases from 8 to 2.5 nm. The selectivity of phenylacetylene hydrogenation correlates with the selectivity of phenylacetylene adsorption on Au/γ-Al2O3 from the phenylacetylene-styrene mixture.

Hydrocarbon Adsorption on Gold Clusters: Experiment and Quantum Chemical Modeling

Heats of adsorption Q of n-alkanes C6–C9 on ZrO2 modified with gold and nickel nanoparticles were determined experimentally. The Q values were found to be higher on average by 7 kJ/mol on the modified samples as compared to the pure support. Density functional theory with the PBE functional and the pseudopotential for gold effectively allowing for relativistic corrections was used to model the adsorption of saturated hydrocarbons on Au and Au + Ni, as exemplified by the interaction of alkanes C1–C3 with Aum, Aum − 1Ni (m = 3, 4, 5) clusters as well as the interaction of C1–C8 with Au20. Based on the calculation results, the probable coordination centers of alkanes on nanoparticle surfaces were found to be vertices and edges, whereas face localization was less probable.

The adsorption properties of titanium dioxide

The adsorption properties of titanium dioxide were studied by gas chromatography. We used organic compounds from different classes, namely, n-alkanes, n-alkenes (C6-C8), and polar compounds (electron donors and acceptors) as test adsorbates. The differential heats of adsorption and the contributions of dispersion and specific intermolecular interaction energies were determined for the systems from the experimental retention data. The electron-donor and electron-acceptor characteristics of the ultimately hydroxylated surface of TiO2 were evaluated.

Influence of the concentration of adsorbate and modifier in the mobile phase on retention in high-performance liquid chromatography

Abstract A method for the determination of the monomolecular adsorption constants from binary (adsorbate–eluent) solution directly from chromatography data (retention volume and concentration) is suggested. The constants of the adsorption equation are calculated from an anisole chromatogram measured on hydroxylated silica using n -hexane in the low concentration region. The adsorption isotherm of anisole is constructed. Good agreement between isotherms calculated by the suggested and by Glueckaufs methods is shown. The influence of the modifier concentration on retention of benzene derivatives is studied for the chromatographic system: n -hexane–tetrahydrofuran–aminopropyl silica. The deviation from linear dependence of the reciprocal of the retention volume on mole fraction of the polar modifier is explained by molecular modifier–modifier interaction in eluent. Taking into account this interaction and using the quasi-chemical model of retention allows one to describe the dependence of chromatographic data of benzene derivatives on the modifier concentration in the eluent.

Adsorption properties of immobilized metal nanoparticles

The adsorption properties of the original TiO2, MgO, and SiO2 surfaces and those modified with nanoscale gold and nickel particles are studied using the dynamic sorption in a range of low coverages. N-alkanes (C6–C9) and adsorbate molecules with different donor and acceptor properties were taken as the reference compounds. Differential molar heats of adsorption of the adsorbates (Qν) are determined from the experimental retention data and, in the case of polar adsorbates, contributions from the dispersion and specific interactions to Qν are found. Donor and acceptor characteristics of the original and modified oxide surfaces are estimated. The immobilization of gold and nickel nanoparticles is shown to result in the formation of less active donor (KD) and acceptor (KA) sites compared to those on the original substrate surfaces. Changes in the surface chemistry and adsorption properties of Au/SiO2 composites compared to the original substrate are less pronounced than in the case of Au,Ni/TiO2 and Au,Ni/MgO composites.

Molecular interactions in liquid chromatography

Abstract An approach to the description of molecular interactions in normal- and reversed-phase high-performance liquid chromatography as quasi-chemical equilibria on the sorbent and in solution (of solute—solvent, modifier—sorbent, solute—modifier and modifier—modifier types) is presented. Such an approach is of help in understanding better the role of various parameters of chromatographic systems that determine the retention of substances in HPLC. The mathematical mechanism used is the same to describe the equilibrium distribution of the sorbate between the liquid and solid phases (adsorption mechanism) or between the liquid and bonded phases (absorption mechanism) and the final equations do not take into account the type of mechanism. A general expression correlating the retention of solute molecules with the concentration of the modifying additive of the mobile phase (over a wide range of concentrations) was obtained. Numerous examples have shown that, depending on the prevalence of certain types of interactions, this relationship makes it possible to describe quantitatively and to explain deviations of the retention dependence from linearity.

Adsorption of chlorobenzenes on ultrafine diamond modified with palladium and nickel nanoparticles

Dynamic sorption is used to study the adsorption properties of palladium and nickel nanoparticles immobilized on a surface of ultrafine diamond (UFD). The test adsorbates are n-alkanes (C6-C8), benzene, chloroform, diethyl ether, chlorobenzene, and o-dichlorobenzene. For each adsorbate, the adsorption isotherms are measured, the isosteric heats of adsorption and contributions to them from the energies of dispersion Qdisp and specific (donor-acceptor) Qspec interactions are calculated, and the electron-donor and electron-acceptor characteristics of the surface of the original UFD and the UFDs with immobilized metal nanoparticles are estimated. It is shown that chlorobenzene is sorbed by the physical adsorption mechanisms on the original support and on a sample modified with nickel nanoparticles, and is chemisorbed on a support modified with palladium nanoparticles. The highest heats of chemisorption are obtained on UFD modified with Pd nanoclusters; a surface of UFD modified with Ni nanoclusters is less active with respect to these chlorobenzenes than a surface of unmodified UFD. Benzene, chloroform, and diethyl ether are sorbed on unmodified and modified UFDs by a physical adsorption mechanism; the highest and lowest values of Qspec for these materials are obtained on UFDs modified with Pd and Ni nanoclusters, respectively.

Quantum-chemical study of the effect of oxygen on the formation of active sites of silver clusters during the selective adsorption of hydrocarbons

Density functional theory (PBE with a modified Dirac-Coulomb-Breit Hamiltonian) is used to simulate the adsorption of hydrocarbons (C2H2, C2H4, C2H6) on the surface of a sorbent containing Ag0, Agδ+, and AgO sites. The dynamics of change in the structural characteristics of Agn (n ≤ 10) is analyzed and the adsorption of oxygen on Ag8 and Ag10 is studied to select the adsorption site model. Studying the interaction of hydrocarbons with Ag8, Ag10, Ag10+, Ag10O, and Ag10O2 clusters reveals that the presence of oxygen leads to an increase in the activation of unsaturated hydrocarbons, and the adsorption energy of C2H2 increases tenfold. It is found that the role of adsorbed oxygen is not only to form adsorption sites of hydrocarbons (Agδ+) but also to bind C2H2 and C2H4 directly to the sorbent’s surface.

Sorption of nitrogen-containing aromatic compounds on ultradispersed diamonds

Adsorption of a number of aniline and pyridine derivatives from water-acetonitrile solution on ultradispersed diamonds was investigated using dynamic sorption method. It was shown that the nature of functional substitutes and their position in molecules of nitrogen-containing compounds of pyridine and aniline have a pronounced effect on adsorption on the surface of ultradispersed diamonds. The dependence of chromatographic sorbate retention on the content of mobile phase could be described by a curve with a minimum. Such nonlinear relationship was explained by the change in the ratio of contribution of specific and non-specific interaction to the sorbate retention that was observed on varying the volume content of an organic component in mobile phase. The influence of temperature on sorption of pyridine and aniline derivatives on ultradisperesed diamonds was investigated. The changes in enthalpy and entropy factors of competitive sorption of sorbates were determined.

Studying the adsorption and activation of benzene and chlorobenzene on Ni(12%)/Al2O3 by means of gas chromatography and quantum chemistry

In studying the surface and adsorption properties of Al2O3 and Ni(12%)/Al2O3 with respect to C6H6 and C6H5Cl, it is found that adsorbate-adsorbent interaction is stronger than adsorbate-adsorbate interaction. It is shown that the calculated isosteric heats of adsorption vary in a range of 61 to 45 kJ/mol depending on adsorption magnitude; for Ni(12%)/γ-Al2O3, as in the case of γ-Al2O3, the heat of adsorption of chlorobenzene is higher at low degrees of filling than that of benzene. According to density functional theory quantum-chemical calculations of the structures of complexes (NinC6H5Cl)z and (NinC6H6)z (n = 1, 4; z = −1, 0, +1), a nickel atom can penetrate into C6H5Cl along the C-Cl bond. It is concluded that a negative charge on nickel contributes to the efficient activation of the C-Cl bond and to an increase in the rate of desorption of benzene, a key step in the hydrodechlorination of chlorobenzene.