Comparative analysis of the catalytic behaviour in CO oxidation of iron containing materials obtained by abiotic and biotic methods and after thermal treatment

This work concerns synthesis of iron oxide containing materials by biotic and abiotic methods and comparison of their properties aimed at finding a common point of intersection that may determine a possible replacement of abiotic materials. Biosynthesis comprised Leptothrix genus of bacteria cultivation in growth medium of Adler. Thermal treatment of biomass samples was used in order to approximate synthesis conditions of the biogenic iron oxide material to those of abiotically obtained hematite. The catalytic activity of the samples was measured in the reaction of CO oxidation by two ways: in situ infrared spectroscopy using a diffuse-reflectance measuring chamber of Nicolet 6700 spectrometer high-temperature vacuum accessory and a flow-type glass reactor. Biomass showed low CO conversions up to 200°C but an increase at 250°C was registered by both used methods. This increase was accompanied by phase transformation. Initial catalytic activity was a result of predominant work of lepidocrocite, whereas a higher activity at 250°C was due to formed maghemite. Abiotic hematite was a bit more active below 240°C than a thermally treated biomass sample in flow-type glass reactor experiments. At higher temperatures, both materials demonstrated the same CO conversion. Spent samples did not show any changes of composition. Although the studied samples were synthesized by different methods, which resulted in different original iron oxide phases, their catalytic performance was very close. Thermally treated biomass samples (obtained by cultivation in Adler's medium) could replace chemically obtained iron oxide as a catalyst in the studied reaction

Mechanochemical Preparation and Properties of Nanodimensional Perovskite Materials

The study is focused on the synthesis of $LaMO_3$ (M = Co, Fe, Mn) perovskite materials using combination of precipitation of precursors and mechanical milling at room temperature. Physicochemical properties of products at each step of preparation were studied by powder X-ray diffraction, Mössbauer spectroscopy, infrared spectroscopy (in the middle and far regions) and X-ray photoelectron measurements. As-prepared perovskite powders are composed of nanoparticles with very fine crystallite size (about 15 nm) in all cases. The materials have also high dispersion, high extent of microstrains and high level of oxygen vacancies which is very important in relevance to their use as heterogeneous catalysts

Effect of the support and the reduction temperature on the formation of metallic nickel phase in Ni/silica gel precursors of vegetable oil hydrogenation catalysts

Ni/SiO(2) materials with identical composition (SiO(2)/Ni = 1.0) have been synthesized by precipitation of Ni(NO(3))(2) center dot 6H(2)O solution with Na(2)CO(3) solution on the silica gel, obtained at three different pH values. The present investigation was undertaken in an endeavor to study the effects of the silica gel support type and the reduction temperature on the formation and dispersion of the metallic nickel phase in the reduced Ni/SiO(2) precursors of the vegetable oil hydrogenation catalyst. The physicochemical characterization of the unreduced and reduced precursors has been accomplished appropriately by powder X-ray diffraction, infrared spectroscopy, temperature programmed reduction and H(2)-chemisorption techniques. It can be stated that the texture peculiarities of the silica gels used as supports influence on the crystalline state and distribution of the deposited Ni-containing phases during the preparation of the precursors, on the reduction temperature of the investigated solids as well as on the bulk size and surface dispersion of the arising metallic nickel particles. It was shown that two types of Ni(2+)-species are formed during the synthesis procedure, namely basic nickel carbonate-like and Ni-phyllosilicate with different extent of presence, location and strength of interaction. The different location of these species is supposed to result in various strength of Ni-O and Ni-O-Si interaction, thus determining the overall reducibility of the precursors. It was specified that the Ni(2+)-species are strongly bonded to the surface of the silica gel obtained at neutral pH value and weakly bonded to the surface of those prepared in acidic and alkaline conditions. It was established that the precursor, derivates from the silica gel obtained at alkaline conditions, demonstrates both significant reduction of the Ni2+ ions at 430A degrees C and finely dispersed metallic nickel particles on its surface. High dispersion of the metallic nickel might be the crucial reason for achieving of high activity in the vegetable oil hydrogenation

A study of the dispersity of iron oxide and iron oxide-noble metal (Me=Pd, Pt) supported systems

Samples of one-(Fe) and two-component (Fe-Pd and Fe-Pt) catalysts were prepared by incipient wetness impregnation of four different supports: TiO2 (anatase), gamma-Al2O3, activated carbon, and diatomite. The chosen synthesis conditions resulted in the formation of nanosized supported phases - iron oxide (in the onecomponent samples), or iron oxide - noble metal (in the two-component ones). Different agglomeration degrees of these phases were obtained as a result of thermal treatment. Ultradisperse size of the supported phase was maintained in some samples, while a process of partial agglomeration occurred in others, giving rise to nearly bidisperse (ultra- and highdisperse) supported particles. The different texture of the used supports and their chemical composition are the reasons for the different stability of the nanosized supported phases. The samples were tested as heterogeneous catalysts in total benzene oxidation reaction

Effect of silver modification on structure and catalytic performance of Ni-Mg/diatomite catalysts for edible oil hydrogenation

Silver modified Mg-Ni/diatomite materials with ratios of SiO2/Ni = 1.07 and Mg/Ni = 0.1, differing in Ag content (Ag/Ni = 0.025 and 0.1) were prepared by the precipitation-deposition method. The effects of silver presence and content on the structure, morphology, texture and H2-adsorption capacity of the obtained precursors were studied by X-ray diffraction, scanning electron microscopy, Hg-porosimetry and H2-chemisorption techniques. The catalytic performance of the corresponding catalysts in the soybean oil hydrogenation was investigated. The increase of the silver loading resulted in the development of macroporosity and increase in the total sample porosity. The decrease of both H2-adsorption capacity and hydrogenation activity are related to the metallic silver covering and blocking effects on the Ni2+ species, thus hampering the access of hydrogen. The decrease of hydrogenation activity and favorable limiting of cis-trans isomerization on the silver modified catalyst are explained by Horiuti-Polanyi mechanism based on the assumption that hydrogenation and isomerization proceed at the same active metallic nickel sites via half-hydrogenated intermediates. It was shown that the adjustment of the catalyst composition by changing the content of silver modifier offers the possibility to control the total amount of solid fat content, stearic acid and detrimental trans fatty acids in the hydrogenated derivatives. The catalyst with higher silver content is proposed as a promising candidate for selective edible oil hydrogenation catalyst