Controlling the Distribution of Framework Aluminum in High-Silica Zeolites

摘要

Using CP/MAS, REDOR, and heteronuclear correlation NMR spectroscopy we have investigated the geometrical relationships between the positive charge of organic structure-directing agents and the negative charge in the framework of zeolite ZSM-13. In samples of all-silica and aluminum containing ZSM-12 prepared using benzyltrimethylammonium cations as structure-directing agents (SDA), we have found that the positively charged segment of the SDA is preferentially ordered near the negative framework charge. This results implies that the distribution of Al sites in the zeolite is distinct from the random distribution often assumed for high-silica zeolites. Our results suggest that the distribution of acid sites can be controlled using SDAs with different charge distributions.