Thermochemistry of Heteroatomic Compounds. Enthalpy of Dissolution and Vaporization of Selected Trimethylsilyl Di- and Tetrathiophosphates

Russian Journal of General Chemistry - Enthalpy of vaporization (ΔvapH°) of trimethylsilyl esters of dithio- and tetratiophosphoric acids (RX)2P(S)SSiMe3 (X = O, S) have been determined...     

Density functional model studies of uranyl adsorption on (001) surfaces of kaolinite

The adsorption of uranyl on two types of neutral (001) surfaces of kaolinite, tetrahedral Si(t) and octahedral Al(o), was studied by means of density functional periodic slab model calculations. Various types of model surface complexes, adsorbed at different sites, were optimized and adsorption energies were estimated. As expected, the Si(t) surface was found to be less reactive than the Al(o) surface. At the neutral Al(o) surface, only adsorption at protonated sites is calculated to be exothermic for inner- as well as outer-sphere adsorption complexes, with monodentate coordination being preferred. Adsorption energies as well as structural features of the adsorption complexes are mainly determined by the number of deprotonated surface hydroxyl groups involved. Outer-sphere complexes on both surfaces exhibit a shorter U-O bond to the aqua ligand of uranyl that is in direct contact with the surface than to the other aqua ligands. This splitting of the shell of equatorial U-O bonds is at variance with common expectations for outer-sphere surface complexes of uranyl.     

Misfit Stress Relaxation in α-Ga2O3/α-Al2O3 Heterostructures via Formation of Misfit Dislocations

Physics of the Solid State - A theoretical model of misfit stress relaxation in film/substrate α-Ga2O3/α-Al2O3 heterostructures with allowance for lattice anisotropy of heterostructure...     

Hydrogenation of carbon dioxide in the presence of rhodium catalysts

The results of CO₂ hydrogenation in the presence of the Wilkinson complexes, viz., RhCl₃ and acacRh(CO)₂, at room temperature and excess PPh₃ are presented. The influence of different ions on the catalytic properties of the Rh complexes was studied. Methanol and methyl formate are formed along with formic acid in the presence of an inorganic salt. Ions that are the most active in the formation of formic acid are the least active in methanol formation.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2436–2439, November, 2004.     

Methods for Studies of Reactions on Zeolite Catalysts Occurring by the Hydrocarbon Pool Mechanism

Kinetics and Catalysis - The review considers the сatalytic reactions occurring by the “hydrocarbon pool” mechanism on zeolite catalysts. The main analytical techniques that allow...     

Synthesis of 4-nitroisoxazoline N-oxides

The reaction of some aliphatic diazo compounds with trans-1-phenyl-1,2-dinitroethylene gave the first representatives of 4-nitroisoxazoline N-oxides, which differ from the unknown 3-nitroisoxazoline N-oxides with respect to their individual physical and chemical properties.     

Charge Carrier Traps in a Bulk Gallium Oxide β-Ga2O3

Physics of the Solid State - Bulk β-Ga2O3 samples grown by the Czochralski method are studied. Based on the studies of the absorbed current dynamics and the cathodoluminescence, it is shown...     

Uranyl adsorption on solvated edge surfaces of pyrophyllite: a DFT model study

In a computational study we addressed the adsorption of uranyl UO(2)(2+) on solvated (110) and (010) edge surfaces of pyrophyllite, applying a density functional approach to periodic slab models. We explored bidentate adsorption complexes on various partially deprotonated adsorption sites: octahedral Al(O,OH), tetrahedral Si(O,OH), and mixed AlO-SiO. Aluminol sites were determined to be most favorable on the (110) surface of pyrophyllite, while on the (010) surface mixed AlO-SiO sites are preferred. The structural parameters of all low-energy complexes on both surfaces agree rather well with EXAFS results for the structurally similar mineral montmorillonite. We calculate the average U-O distance to surface and aqua ligand oxygen atoms to increase with the increasing coordination number of uranyl whereas EXAFS results indicate the opposite trend. According to our results, several adsorption species, with different coordination numbers on different edge faces, may coexist on clay minerals. This computational finding rationalizes why earlier spectroscopic studies indicated the existence of more than one adsorption species, whereas a single type of adsorption complex was suggested from most EXAFS results.     

Modeling the acidizing of carbonate formations with account for the occurrence of wormholes

he results of an investigation of hydrochloric acid treatment on micro and macroscales are presented. A petrophysical permeability-porosity dependence used in the averaged mathematical model and taking account of the wormhole formation effect on the level of individual pores is proposed. The values of the surface reaction rate on carbonate rock dissolving in hydrochloric acid are given from the results of laboratory studies. An optimum rate of hydrochloric acid plug injection is estimated and the constraints due to possible transition of the acidizing in the acid breaking of the formation are discussed.