RESUMEN
The crystallization of colloidal silicalite-1 from clear solution is one of the best understood zeolite formation processes. Colloidal silicalite-1 formation involves a self-assembly process in which nanoslabs and nanotablets with a silicalite-1 type connectivity are formed at intermediate stages. During the assembly process, with strongly anisometric particles present, regions appear with orientational correlations, as evidenced with measurements of dynamic light scattering, viscosity, and rotation of polarized light. The presence of such regions rationalizes the unexpected differences between the crystallization kinetics under microgravity and on earth. The discovery of the locally oriented regions sheds new light on currently poorly understood hydrodynamic effects on the zeolite formation processes, such as the influence of stirring on the phases obtained and the subsequent kinetics. Addition of surfactants or polymers modifies the ordering of the zeolitic building units in the correlated regions, and new types of hierarchical materials named zeogrids and zeotiles can be obtained.
RESUMEN
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.
Asunto(s)
Alcanos/química , Aluminio/química , Silicatos/química , Zeolitas/síntesis química , Coloides , Isomerismo , Temperatura , Factores de Tiempo , Zeolitas/químicaAsunto(s)
Ingravidez , Zeolitas/química , Calor , Tamaño de la Partícula , Suspensiones , Factores de TiempoRESUMEN
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.