Effect of calcination temperature on the surface composition of Mo?Fe catalysts for methanol oxidation

XPS studies have revealed a decrease in the concentration of iron atoms on the surface of Mo–Fe catalysts with increasing calcination temperature. From a comparison of chemical analysis and XPS data the Mo/Fe ratios on the surface of catalyst samples at various calcination temperatures have been determined. Comparing the above data with changes in the catalytic activity of the samples examined in methanol oxidation, the conclusion has been made that the active component of the catalysts is a solid solution of molybdenum oxide in ferric molybdate.

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. Mo/Fe . , .

     

Kinetics of the CH2Cl + CH3 and CHCl2 + CH3 radical-radical reactions

The CH2Cl + CH3 (1) and CHCl2 + CH3 (2) cross-radical reactions were studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 301-800 K and bath gas (helium) density (6-12) x 10(16) atom cm(-3). The observed rate constant of reaction 1 can be represented by an Arrhenius expression k1 = 3.93 x 10(-11) exp(91 K/T) cm3 molecule(-1) s(-1) (+/-25%) or as an average temperature-independent value of k1= (4.8 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1). The rate constant of reaction 2 can be expressed as k2= 1.66 x 10(-11) exp(359 K/T) cm3 molecule(-1) s(-1) (+/-25%). C2H4 and C2H3Cl were detected as the primary products of reactions 1 and 2, respectively. The experimental values of the rate constant are in reasonable agreement with the prediction based on the "geometric mean rule." A separate experimental attempt to determine the rate constants of the high-temperature CH2Cl + O2 (10) and CHCl2 + O2 (11) reaction resulted in an upper limit of 1.2 x 10(-16) cm(3) molecule(-1) s(-1) for k10 and k11 at 800 K.     

Strain hardening of alloys with face-centered cubic lattice

A brief review is given of the peculiarities of the strain hardening of face-centered cubic (fee) alloys as compared with pure metals. The fundamental equations connecting the strain hardening characteristics to the quantitative characteristics of the dislocation structure and the slip trace picture are considered in application to alloys with a high friction stress of a nondislocation nature _F. The shape of the strain hardening curves of alloy mono- and polycrystals is analyzed; it is shown that it depends substantially on the stress level F.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 132–150, August, 1976.     

Branching of equilibria of a system of micro/nanostrings at direct currents

Branching of equilibria of a system of three parallel conducting nano/microlayers, which is used to detect changes in the external and internal mechanical and electric characteristics (for example, conductivity, tension force, and gap between layers), has been investigated. A change in the physical parameters may cause asymmetric bending of the outer layers and deformation of the formerly neutral middle layer. By changing the current in one of the outer layers slowly, their initial symmetry (neutrality of the inner layer) can be restored and the change that occurred in the parameters can be determined.     

Energy Transfer from the Upper Triplet States of Aromatic Molecules

The energy transfer from the upper triplet states of diphenylamine, naphthalene and triphenylene to toluene and hexene-1 is studed. Two mechanisms of dissipation transferred energy in solvents are discussed.     

Study of the oxygen exchange kinetics in the nonstoichiometric oxide SrFeO<Subscript>3–δ</Subscript> under isostoichiometric conditions using the oxygen partial pressure relaxation technique

The kinetics of oxygen exchange in the nonstoichiometric strontium ferrite SrFeO_3–δ with the structure of cubic perovskite was studied by the oxygen partial pressure relaxation technique in the isostoichiometric regime at temperatures of 500–900°C in a range of δ from 0.24 to 0.44. An increase in the oxygen nonstoichiometry δ was accompanied by a decrease in the rate of sample relaxation and by an increase in the apparent activation energy of oxygen exchange.     

Photon echoes in single- and trilayer semiconductor films of different nanosized thicknesses and their properties

A femtosecond stimulated photon echo is detected for the first time in thin semiconductor films with thicknesses of 100, 800, and 2400 nm. It is established that relaxation time T ₁ varies with ZnO film thickness, taking values of 0.96, 2.96, and 4.312 ps at thicknesses of 2400, 800, and 100 nm, respectively. For ZnO/Si⁺/Si^? trilayer films, the relaxation time is T ₁ = 12.73 ps.     

A Quantitative Determination of the Interaction of Pentamethylenetetrazole with the Sodium Ion by Sodium-23 NMR

The importance of the sodium ion transport in biological systems is well known. Numerous studies have dealt with compounds which affect ion transport across membrane systems. However, the mechanism of ion transport across the membrane is still not clear. Hence it is of interest to investigate the interaction of the sodium ion with biologically active compounds in a system where the complex membrane is absent. Such a method of investigation must be able to detect very weak interactions. Sodium-23 nuclear magnetic resonance fits well into this classification. This technique has been used by others¹ and by us² to investigate electrolyte solutions and biological or model systems. We have been interested in the chemistry of cyclopolymethy-lenetetrazoles for some time.³ These compounds are characterized by their strong stimulating action on the central nervous system and, in