Influences of Si/Al Ratios on the Mesopore Distributions of Hierarchical MFI Zeolites Synthesized by Organosilane Surfactant

Abstract

The silicon/aluminum ratio is proved to be a key parameter for mesoporosity tuning in the synthesis of hierarchical MFI zeolites by organosilane surfactant. At the fixed synthesis temperature, the mesopore size distribution evolves from a bimodal type to a uniform mode with the increase of Si/Al ratios. Moreover, different Si/Al ratios result in opposite responses of mesopore distributions to the elevation of synthesis temperature. With the elevated temperature from 140 to 150 °C, the mesopore distribution of low-silica MFI zeolites (Si/Algel = 20) evolves from a bimodal type (centered at 4 and 10 nm) to a relatively uniform mode (centered at 8 nm), whereas the high-silica samples (Si/Algel = 40) exhibit a reverse transformation from a uniform mesopore distribution (centered at 3 nm) to a bimodal mode (centered at 4 and 20 nm). This work demonstrates alternative methods for the mesoporosity tuning of organosilane-directed hierarchical zeolites.