Sebastien Kremer

Zeosil nanoslabs: building blocks in nPr(4)N(+)-mediated synthesis of MFI zeolite

Tetrapropylammonium (TPA)-containing precursors are the building blocks in the crystallization of silica. In the first steps slab-shaped silicalite nanoparticles are formed by ordered combination of the precursors. These nanoslabs have MFI-type zeolite framework topology and play a key role in TPA-ion-mediated zeolite crystallization from monomeric and polymeric silica sources.

Silicalite-1 Zeogrid: A New Silica Molecular Sieve with Super- and Ultra-Micropores

Spherical, micrometer-sized particles with a layered structure were obtained by precipitation of a Silicalite-1 zeolite nanoslab suspension upon addition of cetyltrimethylammonium bromide (CTMABr) and subsequent calcination. The material had a specific micropore volume of 0.69 cm3 g–1, distributed over super- and ultra-micropores. The formation process of this peculiar microporous solid was studied using X-ray diffraction (XRD), 29Si MAS NMR spectroscopy, thermogravimetry (TG), and nitrogen adsorption. In the precipitate, the Silicalite-1 nanoslabs were laterally fused into nanoplates and stapled into layers with intercalated surfactant molecules. Removal of the surfactant through calcination caused facial fusion, besides additional lateral fusion, of the nanoplates. Empty spaces left lying laterally between individual nanoplates were responsible for the super-microporosity. The ultra-micropores were zeolitic channels inside the fused nanoplates. The potential of these Silicalite-1 zeogrids as molecular sieves was demonstrated with pulse gas-chromatographic separation of alkane mixtures. The mass-transfer resistance of a packed bed of zeogrid particles was considerably lower than of compacted zeolite powder.

Microgravity effect on the self-organization of silicalite-1 nanoslabs

Abstract The effect of microgravity on the kinetics of the formation of Silicalite-1 from clear nanoslab suspensions has been studied. Samples processed on MAXUS4 have been analyzed ex situ and their particle populations have been compared to references obtained under gravity. Microgravity has an unexpected and strong retarding effect on the aggregation of Silicalite-1 nanoslabs.

n-Alkane hydroconversion on Zeogrid and colloidal ZSM-5 assembled from aluminosilicate nanoslabs of MFI framework type

n-Alkane hydroisomerisation and hydrocracking experiments reveal that ZSM-5 materials synthesized by self-assembly of nanoslabs show different molecular shape selectivity than ZSM-5 synthesized by hydrothermal methods.

02-O-04 - Colloid chemical properties of silicalite-1 nanoslabs

Publisher Summary This chapter discusses the colloid chemical properties of silicalite-1 nanoslabs. Nanoslabs have negative zeta potential and contain occluded and externally adsorbed tetrapropylammonium (TPA). At room temperature, the nanoslabs form physical aggregates that dissociate upon dilution. The formation of these reversible aggregates accelerates silicalite-1 synthesis upon heating. The influence on the crystallization of dilution with water or tetrapropylammonium hydroxide (TPAOH) solution and of salt addition may be attributed to the changes of the nanoslab mobility and of the nanoslab–nanoslab interfaces. The externally adsorbed TPA controls the formation of ordered chemical bonds between nanoslabs in contact and the subsequent crystal formation.

Unexpected microgravity effect during the self-organization of silicalite-1 nanoslabs

Silicalite-1 zeolite was synthesized from clear solutions prepared from tetraethylorthosilicate, tetrapropylammonium hydroxide and water. Crystallization was performed in a unit composing 30 miniautoclaves programmed to heat to 145 or 155°C and to quench sequentially. The synthesis under microgravity condition was conducted aboard the MAXUS 4 sounding rocket. A reference experiment under normal gravity was executed using the same temperature and time profiles. The evolution of the particle size populations was determined using X-ray scattering. The microgravity condition significantly slowed aggregation but did not change the overall aggregation mechanism. Surprisingly, aggregation of the smallest entities, expected to be the least influenced by absence of convection, were most retarded under microgravity conditions. A considerable fraction of the original nanoslabs persisted even at the end of crystallization. An explanation for this unusual microgravity effect was found in the observation of strong physical interaction between groups of individual particles.