Malina Raileanu

Preparation and characterization of alumina supported silicalite membranes by sol–gel hydrothermal method

Two types of unsupported zeolites (silicalite-1 and silicalite-2) and porous alumina discs supports were prepared by the hydrothermal sol–gel synthesis method. The influence of the raw materials used as SiO 2 source, the temperature of the thermal treatment and the presence of the ceramic support on the crystallization of zeolites were studied. The reaction products were characterized by X-ray diffraction (XRD), IR spectroscopy (IR) and scanning electron microscopy (SEM) studies. The SiO2 source had a significant effect on the final zeolite obtained: the use of colloidal silica sol (ZCS) as SiO 2 source in the synthesis led to ZSM-11 (silicalite-2) crystals, while the sodium silicate solution (ZSS) produced the ZSM-5 (silicalite-1) type. The presence of the alumina support influences the crystallization process of ZSM-5, as it improves nucleation and the ordering of the crystals.

Comparison of promoted alkaline-earth oxide catalysts prepared through evaporation and sol-gel methods by their catalytic performance in propane oxidative dehydrogenation

Abstract Alkaline earth oxides (AEO=MgO, CaO, and SrO) doped with 5 mol% Nd 2 O 3 have been synthesised either by evaporation of nitrate solutions and decomposition, or by sol-gel method. The samples have been characterised by chemical analysis, specific surface area measurement, XRD, CO 2 -TPD, and FTIR spectroscopy. Their catalytic properties in propane oxidative dehydrogenation have been studied. According to detailed XRD analyses, solid solution formation took place, leading to structural defects which were agglomerated or dispersed, their relative amounts depending on the preparation procedure and on the alkaline-earth ion size match with Nd 3+ . Relationships between catalyst synthesis conditions, lattice defects, basicity of the solids and catalytic performance are discussed.

Microstructural Characterization of Silicalite Crystals Obtained by Sol-Gel Hydrothermal Method

Zeolite powders (ZSM-5) and films on different porous supports of Al2O3, Al2O3/TiO2 and Al2O3/Cr2O3 were prepared using the hydrothermal sol-gel synthesis. The morphology of the zeolite powders prepared from sodium silicate as raw material used as SiO2 source was characterized to determine the crystallization conditions. To clarify the growth process of the silicalite crystals, the microstructural study was applied to the crystals that formed in the same time as the membranes. Different treatment temperatures and the presence of the ceramic support on the crystallization of zeolites were studied. Both the zeolite powders and the membranes were analyzed by means of XRD, IR and SEM. The XRD data showed powders after the hydrothermal treatment having the characteristic structure of the silicalite; the SEM results showed the effect of the ceramic support on the particle shape and size.

Effect of Precursors and Ultrasounds on the Properties of Some C60-Doped Sol-Gel Silica Materials

C60-doped silica matrices used through out present study have been prepared by sol-gel processing, using different alcoxide precursors, as a silicon oxide source: tetraethoxysilane, phenyltriethoxysilane and a mixture of phenyltriethoxysilane and tetraethoxysilane.