DEALUMINATION OF ZEOLITE-Y BY H4EDTA

Solid-state NMR shows that the treatment of zeolite Y by H4EDTA dealuminates the zeolite framework. Since no extra-framework aluminium is found, all the Al removed from the framework is subsequently washed out of the crystallites in the form of an H4EDTA complex. Unlike with hydrothermal dealumination or treatment with SiCl4, H4EDTA gives defective crystals in which framework vacancies created by the expulsion of aluminium are not healed by silicon from other parts of the framework. The likely reason for this is the slow intracrystalline diffusion of Si(OH)4 at low temperatures. Si-29 CP/MAS NMR and infrared spectra confirm the creation of hydroxyl nests in the zeolitic framework. A small amount of disordered siliceous phase responsible for a low intensity Si-29 MAS NMR shoulder at -110 ppm is produced in the process.