Performance of a zeolite-containing catalyst and catalysts based on noble metals in intermolecular hydrogen transfer between С<Subscript>6</Subscript> hydrocarbons

The activities of a zeolite-containing catalyst and catalysts containing a noble metal in intermolecular hydrogen transfer between С₆ hydrocarbons are compared. The zeolite-containing catalyst is ineffective in hydrogen transfer from cyclohexane to 1-hexene and in cyclohexene conversion at <400°С. Cyclohexene disproportionation at Т < 200°С takes place only over catalysts containing a noble metal. The cyclohexene conversion selectivity depends strongly on the support type. Using deuterated compounds, it has been demonstrated that intermolecular hydrogen transfer via the dehydrogenation–hydrogenation mechanism involves only the initial cyclohexene.     

Spectral-splitting concentrator photovoltaic modules based on AlGaAs/GaAs/GaSb and GaInP/InGaAs(P) solar cells

A concentrator photovoltaic module with sunlight spectral splitting by Fresnel lens and dichroic filters is developed. The photoelectric conversion efficiency of such a module is estimated at a level of 49.4% when three single-junction cells are used and may reach 48.5–50.6% when a tandem two-junction cell is combined with narrow-band cells. Single-junction AlGaAs, GaAs, GaSb, and InGa(P)As solar sells are fabricated by zinc diffusion from the vapor phase into an n-type epitaxial layer. GaInP/GaAs cascade solar cells are prepared by MOS hydride epitaxy. The overall efficiency of the three single-junction solar cells developed for the spectral-splitting module is 38.1% (AM1.5D) at concentration ratio K _c = 200x. The combination of the solar cells with the cascade structure demonstrates an efficiency of 37.9% at concentrations of 400–800 suns. The parameters of the spectral-splitting photovoltaic module are measured. The photovoltaic efficiency of this module reaches 24.7% in the case of three single-junction cells and 27.9% when the two-junction and single-junction cells are combined.     

Atomic force microscopy modified for studying electric properties of thin films and crystals. Review

Probe force microscopy continues growing in popularity as a method for studying surfaces of solids and control over crystals and thin films that are grown on various scientific and industrial setups. New modifications of the method increase the possibilities for recording various characteristics of the objects studied. An important role here is played by “electrical” force microscopy, the various modifications and practical applications of which are considered below, as well as the results obtained by this method.     

Radical degradation of chitosan under the action of a redox system

Degradation of chitosan in solution under the action of redox radical initiators was studied with the aim to prepare chemically oligomers of natural polysaccharides. The influence of temperature on the rate and extent of the process was examined. The optimal ratios of the substrate to initiator and of the reductant to oxidant in the initiating system were determined.     

X-ray fluorescence determination of lanthanum,cerium, praseodymium,and neodymium in technological solutions after preconcentration on DETATA cellulose filters

Sorption of some rare earth elements on filters with immobilized diethylenetriaminetetraacetate (DETATA) groups was studied. It was shown that the elements are quantitatively extracted from solutions with volume of 20–500 mL at pH values ranging between 3.5 and 5.5 and a flow rate from 1 to 8 mL/min. It was proposed to use masking agents such as sulfosalicylic acid and 1,10-phenanthroline for extracting elements from iron-containing solutions. The elements were determined directly on filters by X-ray fluorescence spectroscopy. The calibration dependences were shown to be linear in the concentration range from 2 to 100 μg of rare earth element per filter. The limits of detection of La, Ce, Pr, and Nd calculated on the basis of the 3s criterion in the case of extraction from 100 mL solutions were 0.03, 0.03, 0.01 and 0.01 μg/mL, respectively.     

Preconcentration of anionic forms of chemical elements on filters with anchored quaternary ammonium groups

Sorption of silicomolybdic acid (SMA) and phosphovanadomolybdic acid (PVMA) and arsenic(V), vanadium(V), and chromium(VI) anionic species is studied on cellulose filters with bound quaternary ammonium groups. These heteropoly acids (HPAs) are recovered in quantity on filters from solutions with high salt backgrounds and with high mineral acid concentrations. AsO ₄ ^3? , CrO ₄ ^2? , and VO ₃ ^? anions are sorbed at pH of 3–9. In this case, the ionic strength considerably influences anion recovery. Conditions were found for preconcentrating vanadium, arsenic, and chromium from 250-mL aliquots of aqueous solutions (the preconcentration coefficient was 5 × 10³). A procedure was proposed for the sorption/X-ray fluorescence determination of these elements in high-purity water.     

Tandem transformations of 10-substituted tetrahydrobenzo[b][1,6]naphthyridines resulted from the Michael addition of the nitrogen atom of the tetrahydropyridine fragment to the triple bond of activated alkynes

A reaction of 10-R-substituted tetrahydrobenzo[b][1,6]naphthyridines (R = CN, CONH₂, Me) with dimethyl acetylenedicarboxylate, methyl and ethyl propiolates, and acetylacetylene has been studied. It was found that 1-acryloyl-10-cyanotetrahydrobenzo[b][1,6]naphthyridines are the major products of the reaction of alkyl propiolates with 10-cyano-substituted naphthyridines, whereas the reaction with 10-carbamoyl-substituted naphthyridines gives a mixture of 1-acryloyl-substituted naphthyridines and hexahydrobenzo[b]pyrido[3,4,5-d,e][1,6]naphthyridines. The latter are the only products in the reaction of 10-carbamoyl-substituted naphthyridines with acetylacetylene. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1516–1527, July, 2008.     

Single-crystal structure of Nd5Mo3O16 at T = 30 K

A precision X-ray diffraction study of Nd₅Mo₃O₁₆ single crystals is performed for the first time at 30 K. Measurements in the range from room temperature to 30K showed that the unit-cell parameters and volume change smoothly. The crystal structure at T = 30 K is similar to that at room temperature. The model of splitting of the atomic positions is confirmed.