Micro/Macroporous System: MFI-Type Zeolite Crystals with Embedded Macropores

摘要

Hierarchically organized systems are commonly encountered in our natural environment. Such hierarchical systems are related mostly to structural properties (e.g., stem of trees, bones) or fluid dynamic properties (e.g., in the lung or the blood circle). The ability of these systems to maximize the efficiency of transport processes has always been an inspiration for their implementation in different artificial systems reaching from watering systems up to catalytic reactors. Zeolite crystals can be regarded as an assembly of miniaturized catalytic reactors with their micropores providing large specific surface area, a defined environment of active sites as well as shape selectivity at each single pore entrance. Thus, zeolites belong to the most important catalytic materials used today. However, their utilization in catalysis is limited due to the slow transport of the reacting species within the micropores. In order to minimize these transport limitations, it is highly desirable to reduce the diffusion path lengths. The preparation of either nanozeolites or zeolitic systems with intracrystalline meso- or macropores belongs to the versatile strategies adopted so far to reach the aforementioned goal.