Franziska Scheffler

Transformation of porous glass beads into MFI-type containing beads

Abstract Macroporous glass beads (Na2O–B2O3–SiO2) with a particle diameter of ∼300 μm and an average pore diameter of 92 nm, obtained by the VYCOR-process, were transformed into MFI-type containing beads, that retained the original shape. The conversion was achieved through a hydrothermal treatment with an aqueous mixture of an Al-source (sodium aluminate or aluminum sulfate) and a template (tetrapropylammonium bromide (TPABr) or dipropylamine (DPA)). The resulting products were characterized by X-ray diffraction, 11B MAS NMR, N2-adsoption and SEM. The filtrates were analyzed by ICP-OES. Using two different templates and two kinds of Al-source MFI-type beads with varying properties were obtained. The boron atoms, which are constituents of the glass material, were used as probe atoms for the characterization of the synthesis procedure. With DPA the crystallization took place inside and on the outer surface of the spheres, while TPABr led to a shell like crystallization starting from the outer surface of the glass particles. The type of Al-source influences the pH value of the reaction mixture and varies the Si/B ratio in the obtained products.

In situ 11B MAS NMR study of the synthesis of a boron-containing MFI type zeolite

Abstract The transformation of porous glass spheres into MFI-spheres in a synthesis with low water content (3 moles H2O per mole TO2 with T=Si, B, Al) was observed by in situ 11 B MAS NMR spectroscopy in two synthesis procedures: (i) sealed quartz ampoules containing the reaction mixture were exposed to the reaction temperature in an oven for the reaction time and then put into the spinner and analyzed at room temperature; (ii) sealed quartz ampoules containing the reaction mixture were put into the spinner, then heated up in the rotating spinner to the reaction temperature and analyzed at this temperature in dependence of the reaction time. The yield of crystalline material could be determined by means of the intensity of a narrow signal at −3.7 ppm in the 11 B MAS NMR spectra. A fast exchange exists between three- and four-coordinated boron in solution, and the relative amount of boron in both coordinations can be determined from the value of the chemical shift of the “liquid” boron signal. Thus, information about changes in the basicity of the solution could be obtained in situ from the chemical shift of the liquid boron signal. It could be shown that crystallization of the zeolite takes place with a strongly increased crystallization time under the influence of the about 105-fold of the standard acceleration of gravity.

Zeolite Coatings on Porous Monoliths

Zeolites find various applications in heterogeneous catalysis, microreactor techniques, sorption techniques, ion exchange and more recently in heat pump applications. In common processes zeolites are used as shaped bodies with a size in the millimeter range. Novel processes made it necessary to apply zeolites as coating on inert or reactive bulk or porous substrate materials. In the past fifteen years various methods for zeolite coatings have been developed and adapted to the specific requirements with respect to the process they are to be used and to the specific physical and chemical properties of the support material.

Hydrothermal transformation of porous glass beads into porous glass beads containing zeolite beta (BEA)

Abstract Hydrothermal transformation of porous glass beads into porous glass beads containing zeolite Beta (BEA) is achieved, at 160 °C, using tetraethylammonium hydroxide (TEAOH) as the templating agent. The products were characterised by various techniques. The XRD results indicate that the transformation of porous glass beads into phase-pure zeolite Beta occurs within the SiO 2 /Al 2 O 3 ratios of 50–100. The Light microscopic images indicate that the shape of the starting porous glass beads is preserved during the hydrothermal treatment. SEM reveals that the outer surface of the porous glass beads is completely covered by zeolite Beta crystals. N 2 adsorption isotherm reveals the microporous nature of the zeolite Beta sample obtained from porous glass beads.

Structured SiSiC-zeolite ceramic composites for catalytic applications via a support self-transformation technique

The overall 3-step process for the manufacturing of SiSiC-zeolite structured cellular composites was studied. The process consists of a 2-step procedure for the ceramic monolith fabrication, followed by the functionalisation of the support surface with zeolite coating (3 rd step). SiSiC ceramic monoliths were prepared by reactive Liquid Silicon Infiltration (LSI) of carbon preforms from corrugated cardboard monoliths. The zeolite coating process consisted of a hydrothermal treatment of the SiSiC carrier in an alkaline solution containing the template and the Al-source, while the Si was provided from the ceramic substrate. MFI-type (ZSM-5) zeolite crystals were directly grown on the ceramic supports via a partial Si dissolution (from the SiSiC matrix) and zeolite crystallisation (support self-transformation). Cellular SiSiC-zeolite monoliths possess bimodal (micro-/macro-) porosity and high mechanical, chemical and thermal stabilities.

Chemical and mechanical supported crystallization (CMSC) of MFI-type zeolite on different reactive substrate materials

Abstract The crystallization of MFI-type zeolite on the surface of reactive supports with dense or porous structure was studied. The reactive support has two functions: crystallization of zeolites can take place on the support surface and constituents for zeolite crystallization can be obtained in situ by partial dissolution of the support. The products obtained after crystallization were characterized by X-ray diffractometrie (XRD), scanning electron microscopy (SEM), and nitrogen adsorption. The results show that it is possible to use supports with different chemical composition as well as with different morphology for the crystallization of zeolitic layers by the method of partial transformation of the support into zeolitic structure, and a good adherence was achieved by this direct crystallization method.