V. V. Malakhov

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.

Formation of vanadia-titania oxide catalysts

The formation of vanadia-titania catalysts was studied with a complex of physicochemical methods. The use of highly dispersed anatase with a defect structure results in the formation of coherent boundaries of coalescence of the V2O5 and TiO2 crystallites with the ratio V : Ti =1 : 1 in a wide range of vanadium and titanium concentrations. The catalysts containing coherent boundaries are active and selective in Β-picoline oxidation to nicotinic acid.

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.

Dynamics of Structural Transformations in the Reduction of Copper Aluminate

The dynamics of structural transformations during copper aluminate reduction in the temperature range used for catalyst activation was studied by high-temperature X-ray analysis under controlled conditions (hydrogen, 2O–4OO‡C). The techniques of neutron diffraction analysis, IR spectroscopy, chemical phase analysis, and electron microscopy were also used at particular stages. In the course of reduction, copper metal is deposited onto the surface of spinel crystals from the bulk. Spinel becomes cation-deficient with respect to copper. An analysis of powder diffraction patterns demonstrated that copper is reduced and released from tetrahedral positions of the spinel structure at temperatures below ~300‡C and from octahedral positions only at temperatures above 300‡C. In this case, a redistribution of aluminum ions was observed simultaneously. It is likely that the electrical neutrality is attained by the formation of OH groups, the appearance of which in reduced samples was detected by IR spectroscopy and confirmed by neutron diffraction analysis. At a reduction temperature of 400‡C, the oxygen framework was partially disintegrated. The structures of reduced copper aluminates and chromites were compared.

Interaction of Hydrogen with Copper-Containing Oxide Catalysts: V. Structural Transformations in Copper Chromite during Reduction–Reoxidation

High-precision X-ray powder diffraction and differential dissolution methods are used to show that copper chromite with a structure of tetragonal spinel is recovered under certain conditions upon the reoxidation of the system of phases formed by the reduction of the initial copper chromite, cation-deficient spinel stabilized by hydrogen and Cu0 particles epitaxially bound to its surface at 250–350°C. However, because of destruction of the initial surface layer at the initial moment of reduction, equilibrium cannot be complete: reoxidized spinel is nonstoichiometric and contains some lattice oxygen-bound protons, and the copper oxide is formed on the surface in some amount. The difference in the phase transition of copper chromite during reduction–reoxidation from the reversible polymorphic transitions characteristic of copper chromite during temperature variations is analyzed.

Oxidative ammonolysis of methylpyrazine over binary catalytic systems: III. Phosphorus-molybdenum system: Catalytic properties and the active component

The phase composition of the binary phosphorus-molybdenum system with a Mo/P ratio of 3-24.5 and its catalytic properties in the reaction of oxidative ammonolysis of methylpyrazine are studied. X-ray amorphous phases of molybdenyl phosphate and phosphorus modified molybdenum trioxide are active in the formation of pyrazinonitrilee.

Calculations and interpretation of the results of stoichiographic analysis of solid multi-element multi-phase compounds and materials

Methods and approaches to the calculations and interpretation of the results of stoichiographic analysis of solid multi-element multi-phase compounds and materials using the flow mode of the differential dissolution (DD) method are reported. Special features of calculationls as well as the objective reasons for the necessity of obtaining more or less precise results of stoichiographic calculations are discussed. The details of the procedure of stoichiographic calculations, refinement, and interpretation of the results are considered on an example of the DD-analysis of the Co-Ni-Fe-Bi-K-P-Mo-O/SiO2-catalyst for the selective oxidation and oxidative ammonolysis of hydrocarbons. The specific details and methods used for the estimation of the performance characteristics of the DD analytical procedure are discussed.

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.

Specific features of the dynamic mode of differential dissolution as of a method of phase analysis

The author considers the specific features of the separation properties of the stoichiographic method of differential dissolution (DD) and the role of thermodynamic and kinetic factors in the processes of the separation of solid mixtures. It is shown that the separation properties of DD should be characterized by selectivity and efficiency, as it is accepted in chromatography. The separation possibilities of DD are considered in characterizing uniformity, stoichiometry-nonstoichiometry of the elemental composition of phases, and also of their macro- and microstructures. The comparison of the principles and characteristics of DD, voltammetry, titrimetry, mass spectroscopy, and chromatography has led to the conclusion that the place of DD among the other methods is determined, primarily, by its unique property, namely, its standardless nature.

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.