Elżbieta Bielańska

Cr-doped Zr, Si-mesoporous molecular sieves as catalysts of CH2Cl2 oxidation

Abstract Zirconium-containing mesoporous silica of nominal Si/Zr ratio in the range 40–5 have been synthesized using dodecylamine as a structure-directing surfactant. The samples were characterized with PXRD, SEM/EDX, BET, CEC measurement and chemical analysis. The materials were used as supports for chromium species incorporated by means of cation exchange procedure. Gradual substitution of Si by Zr in the mesoporous framework results in an increasing structural disorder, increasing cation exchange capacity and increasing capacity for incorporation of Cr. All Cr-doped ZrMMS x catalysts are active in the deep oxidation of methylene chloride reaching 100% conversion at temperature ≥400°C. The catalytic performance depends strongly on the catalyst composition. The role of particular components in determining the catalytic activity and selectivities to various products is discussed.

Hematite nanoparticle monolayers on mica preparation by controlled self-assembly.

A stable suspension of α-Fe(2)O(3) (hematite) was synthesized according to the method of Matijevic and Scheiner by an acidic hydrolysis of ferric chloride. The average size of the particles was determined by dynamic light scattering (DLS) and atomic force microscopy (AFM) and was 22 nm. The electrophoretic mobility and zeta potential of particles were determined as a function of ionic strength and pH. The zeta potential of the hematite particles was positive for pH<8.9 (isoelectric point) and negative otherwise. Using the suspension, systematic studies of particle deposition kinetics on mica were carried out. The coverage of self-assembled particle monolayers was determined by AFM and SEM imaging. Particle deposition was diffusion controlled, with the initial rate proportional to the bulk concentration of particles. On the other hand, for long times, the saturation coverage was attained, increasing systematically with ionic strength. The deposition kinetic runs were adequately reflected by the random sequential adsorption (RSA) model. Additionally, particle desorption kinetics, from previously formed monolayers, were studied using the AFM and SEM methods. It was confirmed that hematite particle desorption was practically negligible within the time period of 60 h. Our experimental data proved, therefore, that it is feasible to produce uniform and stable hematite particle monolayers of desired coverage in self-assembly processes controlled by the bulk suspension concentration and the ionic strength.

Hematite/silver nanoparticle bilayers on mica--AFM, SEM and streaming potential studies.

Bilayers of hematite/silver nanoparticles were obtained in the self-assembly process and thoroughly characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and in situ streaming potential measurements. The hematite nanoparticles, forming a supporting layer, were 22 nm in diameter, exhibiting an isoelectric point at pH 8.9. The silver nanoparticles, used to obtain an external layer, were 29 nm in diameter, and remained negative within the pH range 3 to 11. In order to investigate the particle deposition, mica sheets were used as a model solid substrate. The coverage of the supporting layer was adjusted by changing the bulk concentration of the hematite suspension and the deposition time. Afterward, silver nanoparticle monolayers of controlled coverage were deposited under the diffusion-controlled transport. The coverage of bilayers was determined by a direct enumeration of deposited particles from SEM micrographs and AFM images. Additionally, the formation of the hematite/silver bilayers was investigated by streaming potential measurements carried out under in situ conditions. The effect of the mica substrate and the coverage of a supporting layer on the zeta potential of bilayers was systematically studied. It was established that for the coverage exceeding 0.20, the zeta potential of bilayers was independent on the substrate and the supporting layer coverage. This behavior was theoretically interpreted in terms of the 3D electrokinetic model. Beside significance for basic sciences, these measurements allowed to develop a robust method of preparing nanoparticle bilayers of controlled properties, having potential applications in catalytic processes.

Study of the thermal stability of phases in the Mg-Al system

A part of the Al-Mg phase diagram was studied in the range of composition between 48 and 61 at.% Al by DSC and SEM/EDS methods. The temperature ranges of stability of the β, γ, and ɛ phases were considered. It was found that the congruent melting temperature of the β phase was 450±1 °C. The Al content in that phase was determined to be 61±1 at.% Al at 420 °C. The upper temperature limit of the stability of the ɛ phase was established to be 427±1 °C. The Al content changed from 54 at.% at 390 °C to 56 at.% at 420 °C. The lower temperature limit of the ɛ phase formation was not determined, as a result of a slow ɛ=β+γ reaction. The hypothetical λ or ζ phases were not found, but it was observed that decomposition of oxides might produce extra thermal effects.

Synthesis and characterization of Cu-MFI catalyst for the direct medium temperature range NO decomposition

Abstract In this study the physico-chemical and catalytic properties of copper bearing MFI zeolites (Cu-MFI) with different Si/Al and Si/Cu ratios were investigated. Two different methods for incorporation of metal ions into the zeolite framework were used: the ion exchange from the solution of copper acetate and the direct hydrothermal synthesis. Direct synthesis of a zeolite in the presence of copper-phosphate complexes was expected to generate more active copper species necessary for the desired reaction than the conventional ion exchange method. Direct decomposition of NO was used as a model reaction, because this reaction still offers a very attractive approach to NOX removal. The catalytic properties of zeolite samples were studied using techniques, such as XRD, SEM, EPR and nitrogen adsorption/desorption measurements at 77 K. Results of the kinetic investigation revealed that both methods are applicable for the preparation of the catalysts with active sites capable of catalyzing the NO decomposition. It was found out that Cu-MFI zeolites obtained through direct synthesis are promising catalysts for NO decomposition, especially at lower reaction temperatures. The efficiency of the catalysts prepared by both methods is compared and discussed.

Oxidation of acid-proof steel foil as a method of deposition of phases active in nitrogen oxides decomposition on metallic monolith walls

Pieces of 1H18N9T acid-proof steel foil were subjected to thermoprogrammed oxidation up to 823K, 873K, 1023K and 1113K in air flow. The phases in the oxide layers were determined by Raman spectroscopy. The chemical compositions of the surface microlayers of oxidized foils were investigated by energy dispersive X-ray spectrometry and the chemical compositions of their surface nanolayers were determined by X-ray photoelectron spectrometry. The affinity to oxygen of the foil components was found to be a main factor determining chemical composition and phase structure of the oxides.

Experimental and calculated phase equlibria in the cubic BN-Ta-C system

Theoretical and experimental studies of cubic BN mixed with Ta and TaC in the 1:1 molar ratio are presented. From theoretical calculations it follows that Ta reacts with boron nitride forming additionally two phases: tantalum boride and tantalum nitride. Experimental cBN-phase composites were prepared by high pressure hot pressing. The samples were characterized after heat treatment using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part II: Hydration of δ-Na2Si2O5 and α-Na2Si2O5

Layered Sodium Disilicates as Precursors of Mesoporous Silicas. Part II: Hydration of δ-Na2Si2O5 and α-Na2Si2O5 Reaction of δ-Na2Si2O5 and α-Na2Si2O5 with water at ambient conditions has been studied. The first substrate produced kanemite, the other a crystalline solid, assumed to be the layered hydrated α phase of yet unknown structure. Important differences have been observed in the kinetics of δ-Na2Si2O5 and α-Na2Si2O5 reactions with water, the phase transformation of the latter being distinctly slower. The observed different rates of hydration were associated with the different structural properties of the disilicates investigated. Hydrated δ-Na2Si2O5 and α-Na2Si2O5 possess, respectively, the platy and the needle-like morphology. Hydrated α-Na2Si2O5 contains less interlayer water, which is considered the reason for basal spacing being lower than that of kanemite. The interlayer water trapped between the layers of hydrated α-Na2Si2O5 is more strongly bound than that in kanemite. Warstwowe krzemiany sodu jako prekursory mezoporowatych krzemionek. II: Hydratacja δ-Na2Si2O5 i α-Na2Si2O5 Reakcje δ-Na2Si2O5 i α-Na2Si2O5 z wodą prowadzą do powstania uwodnionych krzemianów sodu, odpowiednio - kanemitu (z fazy δ-Na2Si2O5) i z fazy α - jej uwodnionej formy o nieznanej strukturze. Kinetyki hydratacji tych krzemianów są zdecydowanie różne; faza δ ulega szybkiej transformacji, faza α - wolnej. Różne szybkości hydratacji można wiązać z różnicami strukturalnymi obu krzemianów sodu. Uwodniony δ-Na2Si2O5 wykształcony jest w formie płytek, podczas gdy uwodniony α-Na2Si2O5 ma morfologię typu igieł. Różna jest również ilość wody międzypakietowej w obu hydratach; uwodniony δ-Na2Si2O5 posiada jej więcej ale słabiej związanej, natomiast uwodniony α-Na2Si2O5 mniej, lecz związanej silniej.