The Energetics of Surfactant-Templating of Zeolites

Mesoporosity can be conveniently introduced into zeolites by treating them in basic surfactant solutions. The apparent activation energy involved in the formation of mesopores in USY by surfactant-templating was determined using a combination of in situ synchrotron X-ray diffraction and ex situ gas adsorption. Additionally, techniques such as pH measurement and thermogravimetry/differential thermal analysis were employed to determine OH^- evolution and cetyltrimethylammonium ion (CTA⁺ ) uptake during the development of mesoporosity, thereby providing information about the different steps involved. The combination of both in situ and ex situ techniques has allowed determination of the apparent activation energies of the different processes involved in the mesostructuring of USY zeolites for the first time. Apparent activation energies are of the same order of magnitude (30-65 kJ mol^-1 ) as those involved in the crystallization of zeolites. Hence, important mechanistic insight into the surfactant-templating method was obtained.