Characterization of the porosity in SBA-15 silicas by hyperpolarized 129Xe NMR

SBA-15 samples prepared at several different temperatures are characterized by hyperpolarized Xe-129 NMR spectroscopy. The slope of the chemical shift dependence on pressure allows an evaluation of the xenon-xenon interactions and the size of the micropores at the surface of the SBA-15 mesopores. Samples prepared at 60 degreesC present micropores larger than 8 A. Micropore size gradually decreases with the temperature of synthesis, although some surface roughness can be detected even on samples prepared at 130 degreesC. The decrease of the micropore size with the temperature of synthesis corresponds to a stronger interaction of the adsorbed xenon with the surface. This result is supported by a change of adsorption mechanism as well as by the adsorption enthalpies evaluated from the variation of the Xe-129 chemical shift with temperature.