Innovations in hierarchical zeolite synthesisKe

There has been growing interest in the research and development of hierarchical zeolites possessing at least two levels of porosity in order to reduce diffusion limitations in reactions catalyzed by microporous zeolites. Engineering and manipulation of the hierarchy of pore structures are required to facilitate transport of large reactants and to improve the accessibility of active sites in zeolite catalysts. Various strategies and approaches have been proposed and developed in order to introduce secondary porosity, which is usually in the mesopore range, for conventional zeolites. From controllable post-synthetic modifications to designed direct synthesis with or without mesopore templating agents, significant progress has been made over the past several years in making hierarchical zeolites. In this paper, recent innovations in the synthesis of hierarchical zeolites by different methods will be reviewed, including post-synthetic demetallation, hard-and soft-templating approaches, and template-free routes. We will also discuss separately the progress of hierarchical structures derived from two-dimensional (2D) zeolite nanosheets.A summary and outlook will also be discussed with the focus on providing industrial perspectives of this field. (C) 2015 Elsevier B.V. All rights reserved.