O. V. Bukhtenko

Study of cumene oxidation over zirconia-, titania- and alumina-based complex oxides obtained by sol-gel methods: activity-structure relationships

Abstract Activity-structure relationships have been studied in the low temperature liquid phase cumene oxidation over Fe O/ZrO 2 , Fe O/TiO 2 and Fe O/Al 2 O 3 complex oxides obtained by sol-gel methods. The study has been carried out by the measurements of overall kinetics, product distribution and by X-ray diffraction and Mossbauer spectroscopic methods. Kinetic study in the presence of homogeneous initiator (azo-bis-diazobutyronitrile) has led to the conclusion that the active surface of complex oxides participates in chain initiation most probably via R H bond rupture. Three groups of complex oxides are described: (1) two-phase polycrystalline zirconia-based catalysts showing high activity at low iron loading; (2) one-phase polycrystalline zirconia- and titania-based catalysts exhibiting either activity drop at some critical iron content (zirconia) or monotonic activity dependence (titania) on iron loading; (3) amorphous alumina-based catalysts containing γ-ferric oxide clusters and showing monotone activity dependence. Electronically excited terminal Fe O groups related to the surface FeO 6 polyhedra and iron-containing species located at the interface have been suggested as active centers acquiring the anion-radical behavior. When comparing thermodynamically stable titania (anatase) with metastable one-phase zirconia (cubic or tetragonal) as host matrices, the suggestion was introduced that greater activity of zirconia-based catalysts is due to more energy transfer from the host matrix to the particular active center.

Study of the formation mechanism of complex oxides obtained by the sol–gel method: influence of the structure of iron, aluminium and yttrium acetylacetonate precursors on the phase composition of the ZrO2 ceramics

To obtain new effective basic reagents for single-phase ceramic production with the use of alkoxosynthesis methods, three heterometallic iron–yttrium acetylacetonate complexes were originally synthesized by electrochemical anodic dissolution in acetylacetone. By means of X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), magnetic susceptibility and Mossbauer methods, the structure and properties of the new complex oxides were studied. It was shown that for the iron-containing gels and oxides, Fe3+/Y3+ ions participate in the oxide formation mechanism. The sets of interatomic distances found by means of EXAFS in the new iron–yttrium precursor and in the zirconium gel are practically equal. The presence of structure fragments formed by these bonds and especially direct Fe–Y in the precursors allow the formation of single-phase triple ceramic oxides.

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.

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.

Hydrogen Sulfide-Resistant Bifunctional Catalysts for the Steam Reforming of Methane: Activity and Structural Evolution

Results are presented from studying an iron–nickel catalyst for the steam reforming of methane, synthesized by epitaxial coating on the surface of spherical pellets of commercial γ-Al2O3. It is shown the catalyst is resistant to the presence of hydrogen sulfide in a steam–gas mixture. The degree of conversion of methane during reforming is close to equilibrium at a pressure of 2.0 MPa, a temperature of 800°C, a ratio of Н2О: СН4 = 2: 1, a feedstock hourly space velocity (FHSV) of 6000 h−1, and a H2S concentration of 30 ppm. The structural evolution and phase state of the active components of the system are studied via X-ray diffraction analysis, transmission electron microscopy (TEM), and Mössbauer spectroscopy. The formation of paramagnetic iron oxide clusters tightly bound to the structure of the support, and of FeNi3 iron–nickel alloy particles on the surface of the catalyst, is responsible for the polyfunctional properties of the catalyst, which displays high activity in both the steam reforming of methane and the oxidative decomposition of hydrogen sulfide to elemental sulfur.

Structural organization of phosphorus titanate oxides prepared by the alkoxo method and their catalytic activity in ethylene glycol oxyethylation

The relationship of the structural organization and acid-base properties of the surface of phosphorus titanate oxides prepared from tetra-n-butoxytitanium and phosphorous esters with the catalytic activity and selectivity of these materials in ethylene glycol oxyethylation was studied. Single-phase phosphorus-containing oxides synthesized from 2-diethylamido-4-methyl-1,3,2-dioxophosphorinane and diphenyl(methano)phosphocane have strong surface aprotic acid sites and exhibit high catalytic activity with respect to oxyethylation and a record-breaking selectivity in the formation of the lower homolog, diethylene glycol. The last-mentioned fact is a consequence of the sieve effect exerted by the homogeneous porous structure of supermicropores (8—10 Å) of the oxides. An increase in the concentration of the strong acid sites (≥130 kJ mol–1) on the oxide surface enhances the catalytic activity. On the basis of the temperature programmed desorption of ammonia and CO2 and kinetic measurements, a concerted acid-base mechanism was proposed for the catalytic addition of ethylene oxide to ethylene glycol on the phosphorus-titanate surface.

Structure and acid-basic properties of the surface of titanium oxides modified by phosphorus and aluminum and prepared by the alkoxo method

An alkoxo method for the preparatio of single-phase titanium oxides modified by phosphorus and aluminum is proposed and the mechanism of oxide formation is investigated. Structural studies showed that the sizes of the anatase microcrystallite grains and mesopores in the systems are characterized by a uniform distribution. The nature of the modifying agent and the conditions of synthesis influence the interatomic distances and the dimension ofc, the tetragonal unit cell constant of anatase.

Study of iron-containing carbon-supported catalysts for oxidative decomposition of hydrogen sulfide: The activity—structure relationship

Clusters of nonstoichiometric magnetite Fe3O4+δ and pyrrhotite Fe1-xS were shown to be the active structures of iron-containing carbon-supported catalysts for oxidative decomposition of hydrogen sulfide. A model of the surface active centers is discussed in terms of the anion vacancies participating in the reaction.

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;β=106.39(4)°;V=638.6 Å3, 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 [Y1−aFea]n clusters and, probably, superparamagnetic γ-Fe2O3 species. The second oligomeric acetylacetonate complex contains ions of high-spin two-valence iron, yttrium, and finely dispersed ferromagnetic [Y1−aFea)n intermetallide clusters.

Low temperature selective methane activation to alkenes by a new hydrogen-accumulating system

A heterogeneous hydrogen-accumulating system containing porous titanium with 0.4 wt% Ni combined with high-purity titanium chips was tested for methane activation; methane conversion to C1–C4 hydrocarbons reached a value of ca. 20% over this material, working at 450 °C and 10 atm, after methane circulation across the system for 22 h; the split hydrogen was accumulated as TiH2, being in solid solution with porous metallic titanium.