Study of the initial stages of alkoxo synthesis involving Ti(OBu)4 and cyclophosphites

The reactivities of cyclophosphite precursors in alkoxo syntheses involving titanium(iv) tetra(n-butoxide) were studied by ³¹P NMR and IR spectroscopy. 2-Diethylamido-4-methyl-1,3,2-dioxaphosphinane and 4-ethyl-2,6,7-trioxaphosphabicyclo[2.2.2]octane in benzene are inert toward Ti(OBu)₄. Gelation is accompanied by hydrolysis 2-diethylamido-4-methyl-1,3,2-dioxaphosphinane to give the corresponding hydrophosphoryl compound, while 4-ethyl-2,6,7-trioxaphosphabicyclo[2.2.2]octane remains intact during gelation.     

Fe-containing nanoparticles used as effective catalysts of lignin reforming to syngas and hydrogen assisted by microwave irradiation

Active iron-containing nanosized components have been formed on the lignin surface. The metal was deposited on the lignin from an ethanol solution of Fe(acac)₃ and from a colloid solution of iron metal particles obtained beforehand by metal vapor synthesis. These active components are able to absorb microwave radiation and are suitable for microwave-assisted high-rate dehydrogenation and dry reforming of lignin without addition of a carbon adsorbent, as a supplementary radiation absorbing material, to the feedstock. The dependence of the solid lignin heating dynamics on the concentration of supported iron particles was investigated. The threshold Fe concentration equal to 0.5 wt.%, providing the highest rate of sample heating up to the reforming and plasma generation temperature was identified. The microstructure and magnetic properties of iron-containing nanoparticles supported on lignin were studied before and after the reforming. The Fe₃O₄ nanoparticles and also core-shell Fe₃O₄@γ-Fe-С nanostructures are formed during the reforming of lignin samples. The catalytic performance of iron-based nanoparticles toward the lignin conversion is manifested as increasing selectivity to hydrogen and syngas, which reaches 94% at the Fe concentration of 2 wt.%. It was found that with microwave irradiation under argon, hydrogen predominates in the gas. In the СО₂ atmosphere, dry reforming takes place to give syngas with the СО/Н₂ ratio of ~?0.9. In both cases, the degree of hydrogen recovery from lignin reaches 90–94%.

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Graphical abstract The microwave-supported deposition of iron on the lignin surface gives active well defined nanoparticles Fe₃O₄ and also core-shell Fe₃O₄@γ-Fe-С nanostructures. These nanocomponents provide for high-rate microwave-assisted dehydrogenation and dry reforming of lignin.

     

Reaction of nickel,cobalt, and ferric acetylacetonates with aluminum hydroxide

Conclusions Fe, Co, and Ni acetylacetonates react with boehmite aluminum hydroxide upon its formation in a mother liquor containing aluminum alcoholate with separation of mixed metal-containing complexes from solution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1898–1900, August, 1988.The authors express their gratitude to T. I. Khomenko for taking the diffuse reflection spectra and a discussion of the results.     

Synthesis,structure, and magnetic properties of iron — yttrium complexes containing acetylacetonate ligands

Two new compounds have been obtained by the synthesis of heteronuclear iron-yttrium acetylacetonate, using the modified electrochemical dissolution of the [YFe₂] alloy. One of these compounds, with the Fe(acac)₂ · 2H₂O composition, has been studied by X-ray diffraction analysis. X-ray diffraction data: a=11.002(5), b=5.412(2), c=11.179(5) Å;=106.39(4)°;V=638.6 ų, space group P2₁/c, Z=2. According to the data on magnetic susceptibility, Mössbauer spectroscopy, and X-ray electron microanalysis, single crystals of this complex are covered with an amorphous film containing finely dispersed [Y_1–aFe_a]n clusters and, probably, superparamagnetic -Fe₂O₃ species. The second oligomeric acetylacetonate complex contains ions of high-spin two-valence iron, yttrium, and finely dispersed ferromagnetic [Y_1–aFe_a)n intermetallide clusters.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1454–1458, August, 1995.The studies were financially supported by the International Science Foundation (Grants Nos. MI 8000, MI 8300).     

Synthesis and structure of complex metal oxides produced by interaction of iron and nickel acetylacetonates with hydrolysis products of titanium and zirconium alcoholates

The interaction of nickel and iron acetylacetonates with hydrolysis products of titanium and zirconium alcoholates and their mixture has been studied. It was shown that chemical synthesis of organometallic gels followed by heat treatment makes it possible to form complex single-phase binary or ternary oxides. For the first time single-phase metal-containing titanate, zirconate, and titanate-zirconate oxides have been produced and their structure and magnetic and local electronic properties characterized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 295–300, February, 1991.     

Influence of the Nature of Iron, Aluminium and Yttrium Organometallic Nanocluster Precursors on the Formation Mechanism of Ceramic ZrO2 Obtained by Sol-Gel Method

To obtain new effective precursors for single phase ceramic zirconia materials by the alkoxide route, three heterometallic iron-yttrium acetylacetonate complexes were synthesized by electrochemical anodic dissolution in acetylacetone. The structure and properties of the synthesized complex oxides were studied by XRD, EXAFS, magnetic susceptibility and Mössbauer. It was shown that, for iron-containing gels and oxides, Fe³⁺ ions—interchangeably with Y³⁺—participate in the oxide formation mechanism. The sets of interatomic distances found by EXAFS in the iron-yttrium precursor and in the zirconia gel are practically equal. The presence of structure fragments formed by these interactions—and especially by direct Fe-Y bonds in the precursors—allows single-phase triple ceramic oxides to form.     

Catalytic conversions of chloroolefins over iron oxide nanoparticles 1. Isomerization of dichlorobutenes in the presence of iron oxide nanopaticles immobilized on silicas with different structures

The influence of the support nature and electronic state of iron oxide nanoclusters on the catalytic properties of supported systems was studied for dichlorobutene isomerization. A sample with a Fe content of 2.5 wt.% on the activated silica matrix containing Fe^III and Fe^II ions in the paramagnetic state exhibits the highest activity. The activity of iron on silica gel enhances with the appearance of magnetically ordered nanoclusters of γ-iron oxide formed at the iron content on the catalyst as high as 15 wt.%. An increase in the catalyst activity is favored by the formation of two states of iron (Fe^III and Fe^II) that occurs under the synthesis conditions or during the action of a reactant. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1376–1382, June, 2005.     

Structure,Magnetic and Photochemical Properties of Fe–TiO<Subscript>2</Subscript> Nanoparticles Stabilized in Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Matrix

Fe–TiO₂ nanoparticles with Fe concentration from 0.24 to 5 wt % were synthesized in a Al₂O₃ matrix through multiple impregnations from organic solutions of Ti n-butoxide and Fe acetylacetonate. Microstructure, morphology and magnetic properties of the composites were studied using X-ray analysis, transmission electron microscopy, energy-dispersive analysis, Mössbauer spectroscopy and magnetic susceptibility. It was shown that the deposition of the solution with low concentration of Ti n-butoxide leads to the formation of mostly extensive Fe–TiO₂ films with a small fraction of individual Fe–TiO₂ nanoparticles. On the contrary, the increase of Ti n-butoxide concentration results in the formation of a great number of individual Fe–TiO₂ nanoparticles on Al₂O₃. The size of these particles increases from 2–3 nm to 5–8 nm with the increase of Fe content in the samples from 0.24 to 1.0 (wt %). Mössbauer spectroscopy revealed two types of magnetic ions. The first type of paramagnetic Fe³⁺ demonstrate spin–lattice relaxation properties while another one substitutes Ti⁴⁺ in the TiO₂ structure thus forming Fe–TiO₂ stabilized particles in the matrix. According to the magnetic data antiferromagnetic and ferromagnetic types of exchange spin coupling occur in Fe–TiO₂/Al₂O₃ composites. The increase of Fe concentration in the composites from 1 to 5 wt % results in the narrowing of the TiO₂ band gap from 3.2 to 2.7 eV and shifting the absorption edge in visual spectrum from 350–400 to 450–500 nm.     

Oxidation of CO in microchannels of ceramic membranes modified with oxide catalytic coatings

Ceramic and cermet membranes containing catalytic coatings in the internal volume of their channels were obtained. A relationship between the permeability and kinetic regularities of CO oxidation describing the transmembrane flow of gases was studied. The pre-exponential factor and apparent activation energy change as the loading of the membrane channels by the catalyst proceeds. The study of gas permeability through the membranes showed that the catalyst with a loose branched surface is distributed in the membrane microchannels. The reaction rate constant increases in parallel with an increase in the relative fraction of the catalyst surface. The CO oxidation rate is assumed to depend statistically on the number of active sites, which increases with filling of the membrane channels by the catalytic material.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2613–2619, December, 2004.