Structural Engineering of Hierarchical Zeolite-Based Catalysts

Abstract

Zeolites are important inorganic crystalline materials with unique microporous structures, intrinsic acidic sites, and high hydrothermal stabilities, which have been widely used in the catalytic field such as methanol conversion, catalytic cracking, and NO_x removal. Although the regular channel structures afford zeolite catalysts excellent shape selectivity, the diffusion hindrance caused by the narrow pores (typically less than 2 nm) significantly limits their catalytic activities and lifetimes. Introducing secondary mesopores (2–50 nm) and/or macropores (>50 nm) into the micropore system of zeolites can significantly reduce diffusion limitations and enhance the exposure of more active sites. On the other hand, the delicate integration of microporous zeolites with other functional porous materials into hierarchical heterostructures could offer enhanced or even new catalytic properties that cannot be achieved with single hierarchical zeolite catalysts. For example, tailored meso-/macroporous materials can be combined with zeolites to create composite heterostructures with controllable hierarchical architectures and spatial distributions of functional components from the nano-/microscale to the macroscale in purposeful ways, thus extending their applicability to more intricate and broad heterogeneous catalytic systems. Therefore, the rational design and synthesis of hierarchical zeolite-based materials, spanning from multilevel nanostructures to monoliths, with fascinating catalytic properties hold great significance in the development of efficient energy and environmental catalytic processes.