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.

In this Account, we summarize our efforts devoted to the structural engineering of zeolite-based catalysts with hierarchical architectures. At first, we present a brief summary of synthesis strategies of hierarchical zeolite-based materials in the nano-/microscale with particular emphasis on innovative approaches we have recently developed, including kinetic-modulated crystallization, anisotropic-kinetics transformation, and regioselective surface assembly strategies. Notably, we also explore the application of three-dimensional (3D) printing technology as a customizable and scalable manufacturing method to fabricate monolithic catalysts with industrialization potential at the macroscale by superassembly of nano-/microsized zeolite and other functional porous materials as structural subunits. Subsequently, we discuss several representative hierarchical zeolite-based catalysts including hierarchical zeolites, along with zeolite@layered double hydroxide (LDH), zeolite@mesoporous carbon, and zeolite@porous SiO₂ hierarchically porous heterostructures. These hierarchical zeolite-based catalysts with multilevel pore structures and chemical composition distributions exhibit enhanced catalytic performances in various catalytic reactions. Finally, we point out the remaining challenges and future perspectives for the fabrication and engineering of innovative hierarchical zeolite-based catalysts. This Account highlights the significance of hierarchical zeolite-based materials and aims to inspire further efforts to the rational design and precise construction of these materials to meet the growing demands for industrial catalytic applications.