Defect Models of As-Made High-Silica Zeolites: Clusters of Hydrogen-Bonds and Their Interaction with the Organic Structure-Directing Agents Determined from 1H Double and Triple Quantum NMR Spectroscopy

Internal defect SiOH and SiO- groups evolve during the structure formation of high-Si zeolites in the presence of a cationic organic structure-directing agent (SDA). These negatively charged defects do not completely disappear upon calcination. Herein we investigate the clustering of defect groups and their location within the pore walls of four zeolites. ZSM-12, ZSM-5, and SSZ-74 have three clustered SiOH groups which are hydrogen-bonded to SiO-, whereas SSZ-24 has only two. These defects interact with the structure-directing quaternary ammonium ions preferably close to the charge center, unless steric shielding is present. The framework topologies of ZSM-12, ZSM-5, and SSZ-24 have connected six-rings where the organics interact with the defects. It is suggested that these six-ring patterns form connectivity defects. SSZ-74 is unique, it does not contain an extended six-ring motif, so vacancy defects form instead.