Influence of the crystallinity of pentasil-type zeolites on their acidity

The acid properties of intermediate products in crystallization of pentasil-type zeolites have been investigated using programmed thermal desorption of ammonia and adsorption of pyridine. It was found that acidity increases with increasing crystallinity due to proton-donor centers. A correlation was established between this change in acidity and methanol TPSR data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 1, pp. 48–51, January–February, 1995.     

Electrochemical reductive breakdown of solid-phase chlorinated rubber in aprotic and aqueous media

A study has been made of the electrochemical reductive breakdown (ECRB) of solid-phase chlorinated butyl rubber (CBR). It has been established that CBR does not accept electrons under conditions of fast sweep of electrode potential; however, with prolonged cathodic polarization of the substrate at the polymer/cathode/solution three-phase boundary, it undergoes reduction and subsequent chemical conversion, including intermolecular cross-linking and breakdown of the macromolecules. The rate of ECRB of the CBR depends on the potential and materials of the cathode, and also on the nature of the solvent. In a aprotic medium, the process of CBR breakdown leads to the formation of long polyconjugated structures that color its surface black in the vicinity of the three-phase boundary. In an aqueous medium, no such color is observed, but the products of ECRB are found to contain conjugated double bonds with a shorter conjugation chain than in the case of the aprotic medium. It has been established that he starting reaction in ECRB of CBR is reduction of the C-Cl bond and subsequent elimination of Cl^–.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 710–715, November–December, 1989.     

Effect of Hydration–Dehydration Processes on the Structure and Porosity of Detemplated Silica Fibers

A study was carried out on the conditions of template removal (calcination or extraction by solvents) and hydration–dehydration processes on the hexagonal structure and porosity of detemplated fibers. The hydration–dehydration cycle leads to a decrease in fiber porosity, especially in fiber detemplation by extraction with surfactant solvents such as ethanol and acetic acid.     

Effect of the nature of the ion-exchange cation on the acidity of ZSM-5 zeolites

The acidic properties of the initial and copper-, cerium-, and cobalt-containing high-silica TsVK and TsVN zeolites of the ZSM-S type with SiO21A1203 ratios of 68 and 37, respectively, were investigated by IR spectroscopy and programmed thermal desorption of ammonia. It was shown that the introduction of copper, cerium, and cobalt cations leads to redistribution of the acid centers in the Ts VK and Ts VN zeolites according to their strength, while hardly changing their overall concentration. The strength of the Brnsted acid centers of CuTsVK, CeTsVN, and CoNTsVK zeolites correlates with their activity in the selective reduction of nitrogen oxides by hydrocarbons.     

Investigation of the reaction of acetone and acetonitrile molecules with the surfaces of metallic catalysts by IR-spectroscopic and quantum chemical methods

IR-spectroscopic and quantum chemical methods have been used to establish that the preferred form of the bonds of acetone and acetonitrile with transition metals are by dative action, in which the d-electrons of the metal are localized on the antibonding ^*-orbitals of the functional groups of these molecules. During adsorption of (CH₃)₂CO it is also possible to form a donor-acceptor complex, when there is a transfer of -electrons from the ketone molecule to the free dorbital of the metal.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 545–552, September–October, 1988.     

Role of Adsorption of Reagents in Reduction of NO by Propene on ZrO2-Based Complex Oxide Systems

We have used IR spectroscopy to study adsorption of NO, propene, and their mixture on Rh-Cr₂O₃/ZrO₂ and Rh-CeO₂/ZrO₂ catalysts at temperatures of 293-623 K. We have established that adsorption and coadsorption of the reagents (NO and C₃H₆) have important differences, depending on the nature of the surface. Weak adsorption interactions of the reaction mixture on Rh-CeO₂/ZrO₂ lead to significantly lower activity of this catalyst in selective catalytic reduction (SCR) of NO by propene.     

Mechanism of interaction of carbon monoxide and synthesis gas with nickel catalyst

By means of thermogravimetry, mass spectrometry, and IR spectroscopy, it has been established that carbon monoxide, under condition similar to those in catalytic hydrogenation, is adsorbed on the surface of transition metals primarily in the molecular form.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 6, pp. 693–698, November–December, 1989.     

IR Spectroscopic Study of the Interaction of Transition Metal Ions with Hydroxyapatite Modified by Potassium Ferrocyanide

IR spectroscopy was used to study the modification of hydroxyapatite by potassium ferrocyanide and the interaction of transition metal ions with the modified adsorbent. The structural changes of hydroxyapatite upon the adsorption of Zn²⁺ ions were studied by X-ray phase analysis. Potassium ferrocyanide was found to interact with the surface hydroxyl groups of hydroxyapatite through the nitrogen unshared electron pair. Co²⁺, Ni²⁺, and Zn²⁺ ions were found to eliminate outer-sphere K⁺ ions of adsorbed ferrocyanide to give Fe²⁺— CN—M²⁺— NC—Fe²⁺ bridging structures. Zn²⁺ cations additionally eliminate a part of the Ca²⁺ ions from structural positions of hydroxyapatite, which leads to the appearance of a two-phase hydroxyapatite–sholzite system with heterogeneous distribution of the Ca²⁺ ions in the mot her mineral phase, while the Zr²⁺ ions are found in the new sholzite phase.     

Characteristics of Template Formation in Silica in Acidic Media

Characteristics of template formation in silica at pH < 0.1 in the presence of a surface active substance (cetyltrimethylammonium bromide or chloride) have been investigated. Depending on the acidity of the reaction medium and some other factors, the synthesis of spontaneously growing particles of templated silica at interfacial surfaces led to the formation of fibers, spirals, spheres, and other forms, most of which appeared as hexagonally ordered bodies of revolution. It is possible to detemplate these forms of silica and to transform them to mesoporous molecular sieves without destroying their structures.     

Effect of the Nature of the Template on Formation of the Spatial Structure of Germanium Dioxide under Sol–Gel Synthesis Conditions

We have synthesized for the first time novel forms of germanium dioxide, templated by micellar structures, with hexagonal and/or lamellar spatial structure. We used an original method for detemplating the synthesized materials. We show that it is possible to use these as the basis for obtaining mesophase sorbents, including mesoporous molecular sieves (MMSs). We note that in each specific case, in synthesis of new nanoperiodic and mesoporous materials, including semiconductors, the determining factor is the correct choice of certain template/framework former systems that match with respect to chemical structure and reactivity.