Effect of Crystal Size on Framework Defects and Water Uptake in Fluoride Mediated Silicalite-1

The relationship between framework defects and crystal size in fluoride mediated silicalite-1 was investigated through nitrogen physisorption, X-ray diffraction, and vapor adsorption of ethanol and water on samples with crystal sizes ranging from 0.4 to 30 μm in the b direction of the silicalite-1 crystals. X-ray diffraction reveals a shift in the lattice system from a predominantly monoclinic phase in smaller crystals to an orthorhombic phase in the larger crystals. 29Si MAS studies reveal minimal differences in framework silanol defect concentration. An H-4 type hysteresis in 77 K N2 adsorption isotherm and BdB-FHH pore size analysis reveal the presence of slit-like pores and a larger average pore size as well as a larger volume fraction of “microfissures” in the larger crystals. Pure vapor adsorption measurements show more than a 2-fold increase in water uptake from 0.21 mmol/g to 0.51 mmol/g from the smallest to largest samples at 308 K near unit activity, while ethanol uptake remains on the order of ...