L. S. Dovlitova

In situ XRD study of nanocrystalline cobalt oxide reduction

The reduction of nanocrystalline cobalt oxide samples (single-phase and supported on γ-Al2O3) was studied using in situ X-ray diffraction (XRD) analysis. The atomic structures of single-phase and supported Co3O4 samples were refined, and the occurrence of cationic vacancies was demonstrated. A set of methods (XRD, temperature-programmed reduction, and differential dissolution) was used to find that the reduction of supported and unsupported model cobalt oxide was considerably different. The single-phase sample was reduced in undiluted hydrogen to cobalt metal with a hexagonal closely packed structure. The reduction of the supported sample (unlike the single-phase sample) occurred through the formation of a crystalline CoO phase to the formation of cobalt metal with a face-centered cubic structure. Interaction of cobalt oxide with the γ-Al2O3 support, which hinders the reduction to cobalt metal, was detected.

Methodology and procedure of the stoichiographic analysis of solid inorganic substances and materials

The technical and experimental aspects of creating the conditions of differential dissolution in a flow stoichiographic system are discussed; the scheme of the experimental apparatus, stoichiograph, is presented. The construction, operation conditions of the main units of the stoichiograph, and sample treatment issues are considered. The principles of the creation and optimization of the conditions of the dynamic differential dissolution for the analysis of compounds and materials of the known and unknown phase composition are discussed: the composition of solvents and temperature, and the principles of their variation in time, including those in the processes of stoichiographic titration.

Formation of active component of MoVTeNb oxide catalyst for selective oxidation and ammoxidation of propane and ethane

Abstract The effect of slurry pH on the formation of active component of MoVTeNbO catalyst for selective (amm)oxidation of ethane and propane has been studied. pH affects the nature and composition of the crude and dry precursors as well as chemical and phase composition of the final catalyst. The most effective catalyst is prepared at pH = 3.0, which is characterized by a maximum content of M1 phase.

Copper ions distribution in synthetic copper-zinc hydrosilicate

Abstract Copper ions distribution in the structure of synthetic copper-zinc hydrosilicate of zincsilite structure, obtained non-hydrothermal synthesis have been studied. Zinesilite is referred to the layered silicates of smectite group and is described by the formula Znx (Zn3-x▪x) [Si4O10](OH)2.nH2O, where Zn3-x – are the ions located in the octahedral positions of layers, formed by two sheets of [Si4O10] tetrahedrons; Znx are zinc ions in the interlayer; ▪x are the cation vacancies. Two types of copper ions were distinguished in accordance with the character of their interaction with hydrogen: (1) – substituting zinc ions in the octahedral positions of layers; (2) – substituting zinc ions in the interlayer. These two types of copper ions display the following properties when reacting with hydrogen: (1) – copper ions in octahedral positions start to be reduced at temperatures 553–573 K, and at 723 K reduction degree is 50% ; (2) – copper ions from interlayer start to be reduced at 503–533 K with a constant energy of activation, and their reduction may be complete at this temperature.

Effect of preparation conditions on the phase composition of the MoVTe(Nb) oxide catalyst for the oxidative conversions of propane

The replacement of expensive propylene by propane, which requires the development of catalysts for the direct oxidation of propane into acrylonitrile, is an important and insufficiently studied problem. Multicomponent MomVnTekNbx oxide systems are promising in one-stage ammoxidation of propane to acrylonitrile. Despite considerable attention of various authors to the preparation methods for these catalysts, the reproducibility of their physicochemical and catalytic properties is low. To optimize the technology of catalyst synthesis, we studied the effect of drying method (evaporation or spray drying) for the aqueous suspension of the initial compounds on the formation of the Mo1V0.3Te0.23(Nb0.12) oxide catalyst. It is shown that the method of drying determines the chemical and phase composition of solid catalyst precursors and the phase composition of the final catalyst in high-temperature treatment. The use of spray drying provides the required physicochemical characteristics of the catalyst (the specific surface area and the phase composition) that determine the high activity and selectivity in the selective conversion of propane. These catalysts contain two crystalline phases: orthorhombic M1 and hexagonal M2 in an optimal ratio of 3: 1.

Influence of the surface layer of hydrated silicon on the stabilization of Co2+ cations in Zr–Si fiberglass materials according to XPS, UV-Vis DRS, and differential dissolution phase analysis

The stabilization of cobalt cations in zirconium–silica fiberglass materials was studied by X-ray photoelectron spectroscopy, ultraviolet visible diffusion reflectance spectroscopy, and a differential dissolution phase analysis. It was found that the commercial Zr–Si fiberglass material contained a layer of hydrated silicon (the depth of 6 nm) on the surface of the glass fibers. Modification of the fiberglass material with cobalt led to its distribution in the fibers mainly in the Co2+ state. It was shown that 90% of cobalt was stabilized on the surface and in the hydrated silicon layer as Co2+ cations in tetrahedral oxygen coordination, while the remaining 10% was distributed non-uniformly in the bulk of the fibers as Co2+ cations in octahedral oxygen coordination.

Determination of the chemical composition of fiberglass silicate materials by the differential dissolution method

The standardless method of differential dissolution (DD) was used for determining the chemical composition of aluminosilicate and zirconium silicate glass-fiber clothes at different stages of their preparation and modification. Conditions for the detection, identification, and quantitative determination of various forms of heterogeneity in the elemental, phase, and surface compositions of these materials are considered. The distribution of the elements that constitute the glass-fiber clothes between various forms—surface ion-exchange (Na), hydrated (Al, Si), and framework (Al, Si) species—was quantitatively determined for the first time.

Effect of thermal treatment conditions on the phase composition and structural characteristics of V-Mo-Nb-O catalysts

The formation of an active phase in V-Mo-Nb oxide catalysts for the selective oxidation and ammoxidation of ethane during thermal treatment in air and in helium was studied using high-temperature in situ and ex situ X-ray diffraction analysis, transmission electron microscopy, IR spectroscopy, and the differential dissolution method. It was found that, in thermal treatment below 500°C, the formation occurred through the same irreversible steps with the formation of a unidimensionally ordered layered compound with structure elements like Mo5O14 regardless of the calcination atmosphere. Above 500°C, the formation of crystalline phases took place; the composition and structure of these phases depended on the atmosphere of thermal treatment. The unidimensionally ordered V-Nb-Mo oxide with structure elements like Mo5O14 exhibited the best catalytic properties.

Methods of stoichiography in geochemistry and mineralogy

Abstract Reported is a novel reference-free technique, based on stoichiography, for the molecular and phase analysis of complex mixtures with unknown compositions. The concept of stoichiography is based on the stoichiometry of mass transfer of the constituents in transient, homogeneous and heterogeneous phase transformation processes. The technique utilizes both the separation of components according to their differential dissolution characteristics as well as the dynamics of the changes in stoichiometry. The detailed study of the dissolution processes has been made possible by the use of a specially designed instrumental system, termed a Stoichiograph, which consists of a high sensitive inductively coupled plasma atomic emission spectrometer as the detector–analyzer. Fundamentals, methodology, and instrumentation of the technique are discussed and its application for the phase analysis of multielement-multiphase samples such as minerals, aerosols, and archaeological materials is demonstrated.

Ammoxidation of methylpyrazine over binary oxide systems : IV. A vanadia-titania system

The catalytic properties of vanadia-titania catalysts in methylpyrazine ammoxidation are studied. The activity monotonically increases on changing the concentration from pure titania to pure vanadia, and the yield of methylpyrazine passes through a broad maximum corresponding to a V2O5 concentration from 10 to 75 wt %. The active sites of binary catalysts contain V5+ cations in a substantially distorted octahedral environment of oxygen atoms, which are strongly bound to anatase, likely due to the formation of V-O-Ti bonds