Synthesis of Hierarchically Porous Zeolites for Catalytic Applications

Introduction Hierarchical pore systems (HPSs) are defined by the different porosity levels in two or multiple length scales. HPSs can be found ubiquitously in nature and human artworks, such as the circularly systems of plants and animals, the cellular shells of diatoms, animal nerve systems, man-made architectures, and traffic systems in modern cities. HPSs are naturally or artificially designed for accommodation of maximum functions in a limited volume or area, and also achievement of their maximum efficiencies (e.g., mass transfer or transportation). One of the most important structural effects of HPS as a catalytic material is the enhanced catalytic lifetime. In recent years, various routes to the HPS-type zeolite materials have been developed for catalytic applications, such as synthesis of zeolite samples with nanocrystalline morphologies (so that they can contain intercrystalline mesopores), layer-by-layer separation of zeolite structure, generation of mesopores within zeolite crystal via etching treatment, and use of nano-template as a mesopore generator during zeolite crystallization [1].