Ethylene production by the oxidative condensation of methane in the presence of MnMW/SiO<Subscript>2</Subscript> catalysts (M = Na,K, and Rb)

The samples of MnMW/SiO₂ (M = Na, K, and Rb) were synthesized using various synthesis methods under varied heat treatment conditions and their physicochemical properties and activity in the reaction of the oxidative condensation of methane (OCM) were studied for the development of an effective catalyst for the resource-saving process of natural gas conversion into ethylene. It was found that the preparation method exerts an effect on the textural characteristics of the samples and the reducing properties of the cations of manganese and tungsten. It was determined that the composition of a W-containing phase depends on the alkali metal, and a ratio between the polymorphous modifications of SiO₂ is controlled by the method of synthesis and the conditions of catalyst heat treatment. It was established that the yield of C₂ hydrocarbons in the OCM reaction increased with the use of incipient wetness impregnation instead of the method of mixing with a suspension for catalyst preparation and with an increase in the catalyst heat treatment temperature from 700 to 1000°C. The optimum composition of the catalyst and the condition of its synthesis were found: 2Mn_0.8Na₃W/SiO₂ obtained by the impregnation method and calcined at 1000°C ensured the yield of target products of ~20% with a CH₄ conversion of ~35% at a reaction temperature of 850°C.     

Synthesis and characterization of Sibunit-supported Pd–Ga,Pd–Zn,and Pd–Ag catalysts for liquid-phase acetylene hydrogenation

Pd/Sibunit and Pd–M/Sibunit (M = Ga, Zn, or Ag) catalysts have been synthesized, and their catalytic properties in liquid-phase acetylene hydrogenation have been investigated. Doping of the palladium catalyst with a metal M leads to the formation of the Pd₂Ga, PdZn, or Pd_0.46Ag_0.54 bimetallic compound. The bimetallic particles are much smaller (1.6–2.0 nm) than the monometallic palladium particles (4.0 nm). Doping with zinc raises the ethylene selectivity by 25% without affecting the activity of the catalyst. Specific features of the effect of each of the dopants on palladium are reported.     

Lanthanide-3d cyanometalate chains Ln(III)-M(III) (Ln=Pr, Nd, Sm, Eu, Gd, Tb; M=Fe) with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz): evidence of ferromagnetic interactions for the Sm(III)-M(III) compounds (M=Fe, Cr)

A series of cyanide-bridged chain mixed Fe(III)/Ln(III) (Ln=Pr, Nd, Sm, Eu, Gd, Tb) complexes with the tridentate ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz) used as a capping group has been prepared. Reactions of tptz and LnCl3 with K3Fe(CN)6 yield a family of air-stable 1-D compounds {[Pr(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Nd(tptz)(H2O)4Fe(CN)6].8H2O}infinity, {[Sm(tptz)(H2O)4Fe(CN)6].8H2O}, {[Eu(tptz)(H2O)4Fe(CN)6].6H2O}infinity, {[Gd(tptz)(H2O)4Fe(CN)6].6H2O}infinity, and {[Tb(tptz)(H2O)4Fe(CN)6].8H2O}infinity. Temperature dependent magnetic susceptibility studies of reveal that in , the Sm(III) and Fe(III) ions are ferromagnetically coupled with 3-D ordering occurring below 3.5 K. The appearance of the frequency dependent out-of-phase signal is explained in terms of an ordering with a spin glass-like behavior. To compare the magnetic behavior of with related compounds, {[Sm(tptz)(H2O)4Co(CN)6].8H2O}infinity and {[La(tptz)(DMF)(H2O)3Fe(CN)6].5H2O}infinity, {[Sm(tmphen)(DMF)3(H2O)Fe(CN)6].2H2O}infinity, {[Sm(tmphen)2(H2O)2Fe(CN)6].MeOH.13H2O}infinity and {[Sm(tmphen)2(H2O)2Cr(CN)6].MeOH.9H2O}infinity with 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen) were also prepared.     

XPS for <Emphasis Type="Italic">in situ</Emphasis> study of the mechanisms of heterogeneous catalytic reactions

The possibility to use X-ray photoelectron spectroscopy (XPS) for in situ studies of the mechanisms of heterogeneous catalytic reactions over the pressure range from ultrahigh vacuum to 100 mbar is considered. The application of this method to investigation of CO adsorption and hydrogenation as well as kinetics and mechanism of methanol transformation on the palladium surface at pressures of 10^?6 mbar to 0.1 mbar is reported.     

In situ XPS and MS study of methanol decomposition and oxidation on Pd(111) under millibar pressure range

The methanol decomposition and oxidation on a Pd(111) single crystal have been investigated in situ using ambient-pressure X-ray photoelectron spectroscopy (XPS) and mass-spectrometry (MS) in the temperature range of 300–600 K. It was found that even in the oxygen presence the methanol decomposition on palladium proceeds through two competitive routes: fast dehydrogenation to CO and H₂, and slow decomposition of methanol via the C–O bond scission. The rate of the second route is significant even in the millibar pressure range, which leads to a blocking of the palladium surface by carbon and to a prevention of the further methanol conversion. As a result, no gas phase products of methanol decomposition were detected by mass-spectrometry at 0.1 mbar CH₃OH in the whole temperature range. The methanol C–O bond scission produces CH_x species, which fast dehydrogenate to atomic carbon even at room temperature and further partially dissolve in the palladium bulk at 400 K with the formation of the PdC_x phase. According to in situ XPS data, the PdC_x phase forms even in the oxygen excess. The application of an in situ XPS–MS technique unambiguously shows a good correlation between a decrease in the surface concentration of all carbon-containing species and the rate of methanol conversion. Since these carbon species have a high reactivity towards oxygen, heating of Pd(111) above 450 K in a methanol–oxygen mixture yields CO, CO₂, and water. The product distribution indicates that the main route of methanol conversion is the dehydrogenation of methanol to CO and hydrogen. However, under the experimental conditions used, hydrogen is completely oxidized to water, while CO is partially oxidized to CO₂. No palladium oxide was detected by XPS in these conditions.     

Changes in the fine structure of polycaprolactam induced by hydrostatic pressure

The effect of high (up to 22,000 atm) hydrostatic pressure on the interplanar spacings and corresponding diffraction maxima in polycaprolactam has been investigated. The observations are interpreted in terms of the compressibility anisotropy relative to the amorphous and crystalline regions of the polymer and possible elastic deformation of the amorphous zones leading to tensile stresses in the crystalline regions that relax as the polymer ages owing to processes associated with changes in the conformations of the macromolecules and the number of crosslinks between segments.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, Vol. 4, No. 4, pp. 579–585, July–August, 1968.     

X-ray and magnetic birefringence studies of some lanthanide metallomesogens with Schiff's base ligands

Low angle X-ray scattering studies have been used to identify the mesophase of some calamitic lanthanide mesogens as smectic A, while magnetic birefringence studies have shown a huge magnetic anisotropy for these complexes.     

Manganese(II) chemistry of a new N3O-donor chelate ligand: synthesis, X-ray structures, and magnetic properties of solvent- and oxalate-bound complexes

The synthesis and characterization of a new N3O donor ligand N-benzyl-N-((6-pivaloylamido-2-pyridyl)methyl)-N-(2-pyridylmethyl)amine (bpppa) is reported. Treatment of bpppa with Mn(II)(ClO4)2.6H2O in acetonitrile solution yielded the mononuclear [(bpppa)Mn(CH3CN)(H2O)](ClO4)2 (1) which was characterized by X-ray crystallography, elemental analysis, IR spectroscopy, mass spectrometry, and a solution magnetic moment measurement. Admixture of equimolar equivalents of bpppa and Mn(II)(ClO4)2.6H2O in methanol solution, followed by addition of 0.5 or 1 equivalents of sodium oxalate, yielded the binuclear complex [{(bpppa)Mn}2([mu]-C2O4)](ClO4)2 (2), which was characterized by X-ray crystallography, elemental analysis, IR spectroscopy, mass spectrometry, and solid-state magnetic measurements. While 1 is mononuclear, the formation of the binuclear oxalate derivative indicates that use of the bpppa ligand does not enable isolation of a complex that is structurally relevant to a proposed 1:1 Mn(II)-oxalate adduct in the catalytic cycle of the oxalate degrading enzyme oxalate decarboxylase.