Composition and Structure Dependent Mesopore/Macropore Formation in Zeolites by Desilication

Mass transfer can be enhanced by introducing mesopores (2–50 nm) or macropores (>50 nm) to zeolites through base leaching. To fully understand the mechanism of pore formation, zeolite crystals within the MFI topology but synthesized under different conditions are studied, exploiting advanced characterization tools, such as electron microscopy, focused ion beam, and ptychographic X-ray computed tomography. The meso-/macropore formation is composition and structure dependent. Aluminum zoning leads to the formation of a crystal with a hollow structure, whereas in a crystal with uniform composition, the defective areas, such as the intergrowth boundaries, are preferentially dissolved with concomitant pore formation. These various leaching behaviors of crystals reflect their diversity in properties, which are primarily determined by synthetic factors, such as whether to use a template or not and to synthesize in either the basic or fluoride medium. Regardless of divergent synthesis procedures, common features regarding pore formation are disclosed as well. The rim of a crystal is more robust compared to its central part, and the generation of pores is not uniform along different crystallographic directions, with more pores being arranged along the (010) direction