CALORIMETRIC MEASUREMENT OF ENERGETICS OF CONFINEMENT OF WATER AND ORGANICS IN PORES IN ZEOLITES AND MESOPOROUS MATERIALS

Organic molecules act as structure directing agents (SDA) for the synthesis of inorganic framework structures, including zeolites and mesoporous materials. When the organic molecule has a close geometric fit to the pore, it is present without additional water molecules around it. For the same organic molecule, as the framework pore size increases, the system is stabilized by addition of water molecules. The role of organics in zeolite synthesis in low temperature geologic environments has not been explored but the common presence of organic molecules, especially associated with oil fields, suggests that they may play a role in the synthesis of complex silicates.

In general three interactions must be considered: SDA hydration, SDA framework interaction, and water framework interaction. The competition among these interactions is expected to be closely balanced, especially when the framework is relatively hydrophobic, as for pure silica and the organic somewhat hydrophilic. This research aims to explore these interactions by calorimetry, with an emphasis on the confinement effects of water, as a function of framework pore size. For the frameworks, two large pore pure silica zeolites (about 1 nm), SSZ-53 and SSZ-59 and several mesoporous silica (MCM-41) samples with 2 to 26 nm pores have been chosen. The organic SDA which has a rigid adamantine hydrocarbon structure, with a cross-section of 0.65 to 0.7 nm, is impregnated into the framework. Diffraction, chemical analysis, and solid-state NMR are also employed to investigate the interactions at an atomic level.